1.1. NETBIOS

NetBIOS runs over the following tranports: TCP/IP; NetBEUI and IPX/SPX. Samba only uses NetBIOS over TCP/IP. For details on the TCP/IP NetBIOS Session Service NetBIOS Datagram Service, and NetBIOS Names, see rfc1001.txt and rfc1002.txt.

NetBEUI is a raw NetBIOS frame protocol implementation that allows NetBIOS datagrams to be sent out over the 'wire' embedded within LLC frames. NetBEUI is not required when using NetBIOS over TCP/IP protocols and it is preferable NOT to install NetBEUI if it can be avoided.

IPX/SPX is also not required when using NetBIOS over TCP/IP, and it is preferable NOT to install the IPX/SPX transport unless you are using Novell servers. At the very least, it is recommended that you do not install 'NetBIOS over IPX/SPX'.

[When installing Windows 95, you will find that NetBEUI and IPX/SPX are installed as the default protocols. This is because they are the simplest to manage: no Windows 95 user-configuration is required].

NetBIOS applications (such as samba) offer their services (for example, SMB file and print sharing) on a NetBIOS name. They must claim this name on the network before doing so. The NetBIOS session service will then accept connections on the application's behalf (on the NetBIOS name claimed by the application). A NetBIOS session between the application and the client can then commence.

NetBIOS names consist of 15 characters plus a 'type' character. This is similar, in concept, to an IP address and a TCP port number, respectively. A NetBIOS-aware application on a host will offer different services under different NetBIOS name types, just as a host will offer different TCP/IP services on different port numbers.

NetBIOS names must be claimed on a network, and must be defended. The use of NetBIOS names is most suitable on a single subnet; a Local Area Network or a Wide Area Network.

NetBIOS names are either UNIQUE or GROUP. Only one application can claim a UNIQUE NetBIOS name on a network.

There are two kinds of NetBIOS Name resolution: Broadcast and Point-to-Point.

1.2. BROADCAST NetBIOS

Clients can claim names, and therefore offer services on successfully claimed names, on their broadcast-isolated subnet. One way to get NetBIOS services (such as browsing: see ftp.microsoft.com/drg/developr/CIFS/browdiff.txt; and SMB file/print sharing: see cifs4.txt) working on a LAN or WAN is to make your routers forward all broadcast packets from TCP/IP ports 137, 138 and 139.

This, however, is not recommended. If you have a large LAN or WAN, you will find that some of your hosts spend 95 percent of their time dealing with broadcast traffic. [If you have IPX/SPX on your LAN or WAN, you will find that this is already happening: a packet analyzer will show, roughly every twelve minutes, great swathes of broadcast traffic!].

1.3. NBNS NetBIOS

rfc1001.txt describes, amongst other things, the implementation and use of, a 'NetBIOS Name Service'. NT/AS offers 'Windows Internet Name Service' which is fully rfc1001/2 compliant, but has had to take specific action with certain NetBIOS names in order to make it useful. (for example, it deals with the registration of <1c> <1d> <1e> names all in different ways. I recommend the reading of the Microsoft WINS Server Help files for full details).

The use of a WINS server cuts down on broadcast network traffic for NetBIOS name resolution. It has the effect of pulling all the broadcast isolated subnets together into a single NetBIOS scope, across your LAN or WAN, while avoiding the use of TCP/IP broadcast packets.

When you have a WINS server on your LAN, WINS clients will be able to contact the WINS server to resolve NetBIOS names. Note that only those WINS clients that have registered with the same WINS server will be visible. The WINS server _can_ have static NetBIOS entries added to its database (usually for security reasons you might want to consider putting your domain controllers or other important servers as static entries, but you should not rely on this as your sole means of security), but for the most part, NetBIOS names are registered dynamically.

This provides some confusion for lots of people, and is worth mentioning here: a Browse Server is NOT a WINS Server, even if these services are implemented in the same application. A Browse Server _needs_ a WINS server because a Browse Server is a WINS client, which is _not_ the same thing].

Clients can claim names, and therefore offer services on successfully claimed names, on their broadcast-isolated subnet. One way to get NetBIOS services (such as browsing: see ftp.microsoft.com/drg/developr/CIFS/browdiff.txt; and SMB file/print sharing: see cifs6.txt) working on a LAN or WAN is to make your routers forward all broadcast packets from TCP/IP ports 137, 138 and 139. You will find, however, if you do this on a large LAN or a WAN, that your network is completely swamped by NetBIOS and browsing packets, which is why WINS was developed to minimise the necessity of broadcast traffic.

WINS Clients therefore claim names from the WINS server. If the WINS server allows them to register a name, the client's NetBIOS session service can then offer services on this name. Other WINS clients will then contact the WINS server to resolve a NetBIOS name.

2.1. Introduction

This document gives a general overview of how Samba works internally. The Samba Team has tried to come up with a model which is the best possible compromise between elegance, portability, security and the constraints imposed by the very messy SMB and CIFS protocol.

It also tries to answer some of the frequently asked questions such as:

1. Is Samba secure when running on Unix? The xyz platform? What about the root priveliges issue?

2. Pros and cons of multithreading in various parts of Samba

3. Why not have a separate process for name resolution, WINS, and browsing?

2.2. Multithreading and Samba

People sometimes tout threads as a uniformly good thing. They are very nice in their place but are quite inappropriate for smbd. nmbd is another matter, and multi-threading it would be very nice.

The short version is that smbd is not multithreaded, and alternative servers that take this approach under Unix (such as Syntax, at the time of writing) suffer tremendous performance penalties and are less robust. nmbd is not threaded either, but this is because it is not possible to do it while keeping code consistent and portable across 35 or more platforms. (This drawback also applies to threading smbd.)

The longer versions is that there are very good reasons for not making smbd multi-threaded. Multi-threading would actually make Samba much slower, less scalable, less portable and much less robust. The fact that we use a separate process for each connection is one of Samba's biggest advantages.

2.3. Threading smbd

A few problems that would arise from a threaded smbd are:

1. It's not only to create threads instead of processes, but you must care about all variables if they have to be thread specific (currently they would be global).

2. if one thread dies (eg. a seg fault) then all threads die. We can immediately throw robustness out the window.

3. many of the system calls we make are blocking. Non-blocking equivalents of many calls are either not available or are awkward (and slow) to use. So while we block in one thread all clients are waiting. Imagine if one share is a slow NFS filesystem and the others are fast, we will end up slowing all clients to the speed of NFS.

4. you can't run as a different uid in different threads. This means we would have to switch uid/gid on _every_ SMB packet. It would be horrendously slow.

5. the per process file descriptor limit would mean that we could only support a limited number of clients.

6. we couldn't use the system locking calls as the locking context of fcntl() is a process, not a thread.

2.4. Threading nmbd

This would be ideal, but gets sunk by portability requirements.

Andrew tried to write a test threads library for nmbd that used only ansi-C constructs (using setjmp and longjmp). Unfortunately some OSes defeat this by restricting longjmp to calling addresses that are shallower than the current address on the stack (apparently AIX does this). This makes a truly portable threads library impossible. So to support all our current platforms we would have to code nmbd both with and without threads, and as the real aim of threads is to make the code clearer we would not have gained anything. (it is a myth that threads make things faster. threading is like recursion, it can make things clear but the same thing can always be done faster by some other method)

Chris tried to spec out a general design that would abstract threading vs separate processes (vs other methods?) and make them accessible through some general API. This doesn't work because of the data sharing requirements of the protocol (packets in the future depending on packets now, etc.) At least, the code would work but would be very clumsy, and besides the fork() type model would never work on Unix. (Is there an OS that it would work on, for nmbd?)

A fork() is cheap, but not nearly cheap enough to do on every UDP packet that arrives. Having a pool of processes is possible but is nasty to program cleanly due to the enormous amount of shared data (in complex structures) between the processes. We can't rely on each platform having a shared memory system.

2.5. nbmd Design

Originally Andrew used recursion to simulate a multi-threaded environment, which use the stack enormously and made for really confusing debugging sessions. Luke Leighton rewrote it to use a queuing system that keeps state information on each packet. The first version used a single structure which was used by all the pending states. As the initialisation of this structure was done by adding arguments, as the functionality developed, it got pretty messy. So, it was replaced with a higher-order function and a pointer to a user-defined memory block. This suddenly made things much simpler: large numbers of functions could be made static, and modularised. This is the same principle as used in NT's kernel, and achieves the same effect as threads, but in a single process.

Then Jeremy rewrote nmbd. The packet data in nmbd isn't what's on the wire. It's a nice format that is very amenable to processing but still keeps the idea of a distinct packet. See "struct packet_struct" in nameserv.h. It has all the detail but none of the on-the-wire mess. This makes it ideal for using in disk or memory-based databases for browsing and WINS support.

3.1. New Output Syntax

The syntax of a debugging log file is represented as:

  >debugfile< :== { >debugmsg< }

  >debugmsg<  :== >debughdr< '\n' >debugtext<

  >debughdr<  :== '[' TIME ',' LEVEL ']' FILE ':' [FUNCTION] '(' LINE ')'

  >debugtext< :== { >debugline< }

  >debugline< :== TEXT '\n'

TEXT is a string of characters excluding the newline character.

LEVEL is the DEBUG level of the message (an integer in the range 0..10).

TIME is a timestamp.

FILE is the name of the file from which the debug message was generated.

FUNCTION is the function from which the debug message was generated.

LINE is the line number of the debug statement that generated the message.

Basically, what that all means is:

1. A debugging log file is made up of debug messages.

2. Each debug message is made up of a header and text. The header is separated from the text by a newline.

3. The header begins with the timestamp and debug level of the message enclosed in brackets. The filename, function, and line number at which the message was generated follow. The filename is terminated by a colon, and the function name is terminated by the parenthesis which contain the line number. Depending upon the compiler, the function name may be missing (it is generated by the __FUNCTION__ macro, which is not universally implemented, dangit).

4. The message text is made up of zero or more lines, each terminated by a newline.

Here's some example output:

    [1998/08/03 12:55:25, 1] nmbd.c:(659)
      Netbios nameserver version 1.9.19-prealpha started.
      Copyright Andrew Tridgell 1994-1997
    [1998/08/03 12:55:25, 3] loadparm.c:(763)
      Initializing global parameters

Note that in the above example the function names are not listed on the header line. That's because the example above was generated on an SGI Indy, and the SGI compiler doesn't support the __FUNCTION__ macro.

3.2. The DEBUG() Macro

Use of the DEBUG() macro is unchanged. DEBUG() takes two parameters. The first is the message level, the second is the body of a function call to the Debug1() function.

That's confusing.

Here's an example which may help a bit. If you would write

printf( "This is a %s message.\n", "debug" );

to send the output to stdout, then you would write

DEBUG( 0, ( "This is a %s message.\n", "debug" ) );

to send the output to the debug file. All of the normal printf() formatting escapes work.

Note that in the above example the DEBUG message level is set to 0. Messages at level 0 always print. Basically, if the message level is less than or equal to the global value DEBUGLEVEL, then the DEBUG statement is processed.

The output of the above example would be something like:

    [1998/07/30 16:00:51, 0] file.c:function(128)
      This is a debug message.

Each call to DEBUG() creates a new header *unless* the output produced by the previous call to DEBUG() did not end with a '\n'. Output to the debug file is passed through a formatting buffer which is flushed every time a newline is encountered. If the buffer is not empty when DEBUG() is called, the new input is simply appended.

...but that's really just a Kludge. It was put in place because DEBUG() has been used to write partial lines. Here's a simple (dumb) example of the kind of thing I'm talking about:

    DEBUG( 0, ("The test returned " ) );
    if( test() )
      DEBUG(0, ("True") );
    else
      DEBUG(0, ("False") );
    DEBUG(0, (".\n") );

Without the format buffer, the output (assuming test() returned true) would look like this:

    [1998/07/30 16:00:51, 0] file.c:function(256)
      The test returned
    [1998/07/30 16:00:51, 0] file.c:function(258)
      True
    [1998/07/30 16:00:51, 0] file.c:function(261)
      .

Which isn't much use. The format buffer kludge fixes this problem.

3.3. The DEBUGADD() Macro

In addition to the kludgey solution to the broken line problem described above, there is a clean solution. The DEBUGADD() macro never generates a header. It will append new text to the current debug message even if the format buffer is empty. The syntax of the DEBUGADD() macro is the same as that of the DEBUG() macro.

    DEBUG( 0, ("This is the first line.\n" ) );
    DEBUGADD( 0, ("This is the second line.\nThis is the third line.\n" ) );

Produces

    [1998/07/30 16:00:51, 0] file.c:function(512)
      This is the first line.
      This is the second line.
      This is the third line.

3.4. The DEBUGLVL() Macro

One of the problems with the DEBUG() macro was that DEBUG() lines tended to get a bit long. Consider this example from nmbd_sendannounce.c:

  DEBUG(3,("send_local_master_announcement: type %x for name %s on subnet %s for workgroup %s\n",
            type, global_myname, subrec->subnet_name, work->work_group));

One solution to this is to break it down using DEBUG() and DEBUGADD(), as follows:

  DEBUG( 3, ( "send_local_master_announcement: " ) );
  DEBUGADD( 3, ( "type %x for name %s ", type, global_myname ) );
  DEBUGADD( 3, ( "on subnet %s ", subrec->subnet_name ) );
  DEBUGADD( 3, ( "for workgroup %s\n", work->work_group ) );

A similar, but arguably nicer approach is to use the DEBUGLVL() macro. This macro returns True if the message level is less than or equal to the global DEBUGLEVEL value, so:

  if( DEBUGLVL( 3 ) )
    {
    dbgtext( "send_local_master_announcement: " );
    dbgtext( "type %x for name %s ", type, global_myname );
    dbgtext( "on subnet %s ", subrec->subnet_name );
    dbgtext( "for workgroup %s\n", work->work_group );
    }

(The dbgtext() function is explained below.)

There are a few advantages to this scheme:

1. The test is performed only once.

2. You can allocate variables off of the stack that will only be used within the DEBUGLVL() block.

3. Processing that is only relevant to debug output can be contained within the DEBUGLVL() block.

3.5. New Functions

5.1. Character Handling

This section describes character set handling in Samba, as implemented in Samba 3.0 and above

In the past Samba had very ad-hoc character set handling. Scattered throughout the code were numerous calls which converted particular strings to/from DOS codepages. The problem is that there was no way of telling if a particular char* is in dos codepage or unix codepage. This led to a nightmare of code that tried to cope with particular cases without handlingt the general case.

5.2. The new functions

The new system works like this:

1. all char* strings inside Samba are "unix" strings. These are multi-byte strings that are in the charset defined by the "unix charset" option in smb.conf.

2. there is no single fixed character set for unix strings, but any character set that is used does need the following properties:

   1. must not contain NULLs except for termination

   2. must be 7-bit compatible with C strings, so that a constant string or character in C will be byte-for-byte identical to the equivalent string in the chosen character set.

   3. when you uppercase or lowercase a string it does not become longer than the original string

   4. must be able to correctly hold all characters that your client will throw at it

   For example, UTF-8 is fine, and most multi-byte asian character sets are fine, but UCS2 could not be used for unix strings as they contain nulls.

3. when you need to put a string into a buffer that will be sent on the wire, or you need a string in a character set format that is compatible with the clients character set then you need to use a pull_ or push_ function. The pull_ functions pull a string from a wire buffer into a (multi-byte) unix string. The push_ functions push a string out to a wire buffer.

4. the two main pull_ and push_ functions you need to understand are pull_string and push_string. These functions take a base pointer that should point at the start of the SMB packet that the string is in. The functions will check the flags field in this packet to automatically determine if the packet is marked as a unicode packet, and they will choose whether to use unicode for this string based on that flag. You may also force this decision using the STR_UNICODE or STR_ASCII flags. For use in smbd/ and libsmb/ there are wrapper functions clistr_ and srvstr_ that call the pull_/push_ functions with the appropriate first argument.

   You may also call the pull_ascii/pull_ucs2 or push_ascii/push_ucs2 functions if you know that a particular string is ascii or unicode. There are also a number of other convenience functions in charcnv.c that call the pull_/push_ functions with particularly common arguments, such as pull_ascii_pstring()

5. The biggest thing to remember is that internal (unix) strings in Samba may now contain multi-byte characters. This means you cannot assume that characters are always 1 byte long. Often this means that you will have to convert strings to ucs2 and back again in order to do some (seemingly) simple task. For examples of how to do this see functions like strchr_m(). I know this is very slow, and we will eventually speed it up but right now we want this stuff correct not fast.

6. all lp_ functions now return unix strings. The magic "DOS" flag on parameters is gone.

7. all vfs functions take unix strings. Don't convert when passing to them

5.3. Macros in byteorder.h

This section describes the macros defined in byteorder.h. These macros are used extensively in the Samba code.

5.4. LAN Manager Samba API

This section describes the functions need to make a LAN Manager RPC call. This information had been obtained by examining the Samba code and the LAN Manager 2.0 API documentation. It should not be considered entirely reliable.

call_api(int prcnt, int drcnt, int mprcnt, int mdrcnt, 
	char *param, char *data, char **rparam, char **rdata);

This function is defined in client.c. It uses an SMB transaction to call a remote api.

5.5. Code character table

Certain data structures are described by means of ASCIIz strings containing code characters. These are the code characters:

1. W a type byte little-endian unsigned integer

2. N a count of substructures which follow

3. D a four byte little-endian unsigned integer

4. B a byte (with optional count expressed as trailing ASCII digits)

5. z a four byte offset to a NULL terminated string

6. l a four byte offset to non-string user data

7. b an offset to data (with count expressed as trailing ASCII digits)

8. r pointer to returned data buffer???

9. L length in bytes of returned data buffer???

10. h number of bytes of information available???

6.1. Lexical Analysis

Basically, the file is processed on a line by line basis. There are four types of lines that are recognized by the lexical analyzer (params.c):

1. Blank lines - Lines containing only whitespace.

2. Comment lines - Lines beginning with either a semi-colon or a pound sign (';' or '#').

3. Section header lines - Lines beginning with an open square bracket ('[').

4. Parameter lines - Lines beginning with any other character. (The default line type.)

The first two are handled exclusively by the lexical analyzer, which ignores them. The latter two line types are scanned for

1. - Section names

2. - Parameter names

3. - Parameter values

These are the only tokens passed to the parameter loader (loadparm.c). Parameter names and values are divided from one another by an equal sign: '='.

	param name = parameter value string \
	with line continuation.

    param name = parameter value string     with line continuation.

	param name = parameter value string \
    \
    with line continuation.

param name = parameter value string         with line continuation.

	param name = parameter value string \
	; comment \
    with a comment.

param name = parameter value string     ; comment     with a comment.

	[ section   name ] garbage \
    param  name  = value

	[section name]
    param name = value

6.2. Syntax

The syntax of the smb.conf file is as follows:

  <file>            :==  { <section> } EOF
  <section>         :==  <section header> { <parameter line> }
  <section header>  :==  '[' NAME ']'
  <parameter line>  :==  NAME '=' VALUE NL

Basically, this means that

1. a file is made up of zero or more sections, and is terminated by an EOF (we knew that).

2. A section is made up of a section header followed by zero or more parameter lines.

3. A section header is identified by an opening bracket and terminated by the closing bracket. The enclosed NAME identifies the section.

4. A parameter line is divided into a NAME and a VALUE. The *first* equal sign on the line separates the NAME from the VALUE. The VALUE is terminated by a newline character (NL = '\n').

7.1. Introduction

This is a short document that describes some of the issues that confront a SMB implementation on unix, and how Samba copes with them. They may help people who are looking at unix<->PC interoperability.

It was written to help out a person who was writing a paper on unix to PC connectivity.

7.2. Usernames

The SMB protocol has only a loose username concept. Early SMB protocols (such as CORE and COREPLUS) have no username concept at all. Even in later protocols clients often attempt operations (particularly printer operations) without first validating a username on the server.

Unix security is based around username/password pairs. A unix box should not allow clients to do any substantive operation without some sort of validation.

The problem mostly manifests itself when the unix server is in "share level" security mode. This is the default mode as the alternative "user level" security mode usually forces a client to connect to the server as the same user for each connected share, which is inconvenient in many sites.

In "share level" security the client normally gives a username in the "session setup" protocol, but does not supply an accompanying password. The client then connects to resources using the "tree connect" protocol, and supplies a password. The problem is that the user on the PC types the username and the password in different contexts, unaware that they need to go together to give access to the server. The username is normally the one the user typed in when they "logged onto" the PC (this assumes Windows for Workgroups). The password is the one they chose when connecting to the disk or printer.

The user often chooses a totally different username for their login as for the drive connection. Often they also want to access different drives as different usernames. The unix server needs some way of divining the correct username to combine with each password.

Samba tries to avoid this problem using several methods. These succeed in the vast majority of cases. The methods include username maps, the service%user syntax, the saving of session setup usernames for later validation and the derivation of the username from the service name (either directly or via the user= option).

7.3. File Ownership

The commonly used SMB protocols have no way of saying "you can't do that because you don't own the file". They have, in fact, no concept of file ownership at all.

This brings up all sorts of interesting problems. For example, when you copy a file to a unix drive, and the file is world writeable but owned by another user the file will transfer correctly but will receive the wrong date. This is because the utime() call under unix only succeeds for the owner of the file, or root, even if the file is world writeable. For security reasons Samba does all file operations as the validated user, not root, so the utime() fails. This can stuff up shared development diectories as programs like "make" will not get file time comparisons right.

There are several possible solutions to this problem, including username mapping, and forcing a specific username for particular shares.

7.4. Passwords

Many SMB clients uppercase passwords before sending them. I have no idea why they do this. Interestingly WfWg uppercases the password only if the server is running a protocol greater than COREPLUS, so obviously it isn't just the data entry routines that are to blame.

Unix passwords are case sensitive. So if users use mixed case passwords they are in trouble.

Samba can try to cope with this by either using the "password level" option which causes Samba to try the offered password with up to the specified number of case changes, or by using the "password server" option which allows Samba to do its validation via another machine (typically a WinNT server).

Samba supports the password encryption method used by SMB clients. Note that the use of password encryption in Microsoft networking leads to password hashes that are "plain text equivalent". This means that it is *VERY* important to ensure that the Samba smbpasswd file containing these password hashes is only readable by the root user. See the documentation ENCRYPTION.txt for more details.

7.5. Locking

Since samba 2.2, samba supports other types of locking as well. This section is outdated.

The locking calls available under a DOS/Windows environment are much richer than those available in unix. This means a unix server (like Samba) choosing to use the standard fcntl() based unix locking calls to implement SMB locking has to improvise a bit.

One major problem is that dos locks can be in a 32 bit (unsigned) range. Unix locking calls are 32 bits, but are signed, giving only a 31 bit range. Unfortunately OLE2 clients use the top bit to select a locking range used for OLE semaphores.

To work around this problem Samba compresses the 32 bit range into 31 bits by appropriate bit shifting. This seems to work but is not ideal. In a future version a separate SMB lockd may be added to cope with the problem.

It also doesn't help that many unix lockd daemons are very buggy and crash at the slightest provocation. They normally go mostly unused in a unix environment because few unix programs use byte range locking. The stress of huge numbers of lock requests from dos/windows clients can kill the daemon on some systems.

The second major problem is the "opportunistic locking" requested by some clients. If a client requests opportunistic locking then it is asking the server to notify it if anyone else tries to do something on the same file, at which time the client will say if it is willing to give up its lock. Unix has no simple way of implementing opportunistic locking, and currently Samba has no support for it.

7.6. Deny Modes

When a SMB client opens a file it asks for a particular "deny mode" to be placed on the file. These modes (DENY_NONE, DENY_READ, DENY_WRITE, DENY_ALL, DENY_FCB and DENY_DOS) specify what actions should be allowed by anyone else who tries to use the file at the same time. If DENY_READ is placed on the file, for example, then any attempt to open the file for reading should fail.

Unix has no equivalent notion. To implement this Samba uses either lock files based on the files inode and placed in a separate lock directory or a shared memory implementation. The lock file method is clumsy and consumes processing and file resources, the shared memory implementation is vastly prefered and is turned on by default for those systems that support it.

7.7. Trapdoor UIDs

A SMB session can run with several uids on the one socket. This happens when a user connects to two shares with different usernames. To cope with this the unix server needs to switch uids within the one process. On some unixes (such as SCO) this is not possible. This means that on those unixes the client is restricted to a single uid.

Note that you can also get the "trapdoor uid" message for other reasons. Please see the FAQ for details.

7.8. Port numbers

There is a convention that clients on sockets use high "unprivilaged" port numbers (>1000) and connect to servers on low "privilaged" port numbers. This is enforced in Unix as non-root users can't open a socket for listening on port numbers less than 1000.

Most PC based SMB clients (such as WfWg and WinNT) don't follow this convention completely. The main culprit is the netbios nameserving on udp port 137. Name query requests come from a source port of 137. This is a problem when you combine it with the common firewalling technique of not allowing incoming packets on low port numbers. This means that these clients can't query a netbios nameserver on the other side of a low port based firewall.

The problem is more severe with netbios node status queries. I've found that WfWg, Win95 and WinNT3.5 all respond to netbios node status queries on port 137 no matter what the source port was in the request. This works between machines that are both using port 137, but it means it's not possible for a unix user to do a node status request to any of these OSes unless they are running as root. The answer comes back, but it goes to port 137 which the unix user can't listen on. Interestingly WinNT3.1 got this right - it sends node status responses back to the source port in the request.

7.9. Protocol Complexity

There are many "protocol levels" in the SMB protocol. It seems that each time new functionality was added to a Microsoft operating system, they added the equivalent functions in a new protocol level of the SMB protocol to "externalise" the new capabilities.

This means the protocol is very "rich", offering many ways of doing each file operation. This means SMB servers need to be complex and large. It also means it is very difficult to make them bug free. It is not just Samba that suffers from this problem, other servers such as WinNT don't support every variation of every call and it has almost certainly been a headache for MS developers to support the myriad of SMB calls that are available.

There are about 65 "top level" operations in the SMB protocol (things like SMBread and SMBwrite). Some of these include hundreds of sub-functions (SMBtrans has at least 120 sub-functions, like DosPrintQAdd and NetSessionEnum). All of them take several options that can change the way they work. Many take dozens of possible "information levels" that change the structures that need to be returned. Samba supports all but 2 of the "top level" functions. It supports only 8 (so far) of the SMBtrans sub-functions. Even NT doesn't support them all.

Samba currently supports up to the "NT LM 0.12" protocol, which is the one preferred by Win95 and WinNT3.5. Luckily this protocol level has a "capabilities" field which specifies which super-duper new-fangled options the server suports. This helps to make the implementation of this protocol level much easier.

There is also a problem with the SMB specications. SMB is a X/Open spec, but the X/Open book is far from ideal, and fails to cover many important issues, leaving much to the imagination. Microsoft recently renamed the SMB protocol CIFS (Common Internet File System) and have published new specifications. These are far superior to the old X/Open documents but there are still undocumented calls and features. This specification is actively being worked on by a CIFS developers mailing list hosted by Microsft.

9.1. Introduction

This document contains information to provide an NT workstation with login services, without the need for an NT server. It is the sgml version of http://mailhost.cb1.com/~lkcl/cifsntdomain.txt, controlled by Luke.

It should be possible to select a domain instead of a workgroup (in the NT workstation's TCP/IP settings) and after the obligatory reboot, type in a username, password, select a domain and successfully log in. I would appreciate any feedback on your experiences with this process, and any comments, corrections and additions to this document.

The packets described here can be easily derived from (and are probably better understood using) Netmon.exe. You will need to use the version of Netmon that matches your system, in order to correctly decode the NETLOGON, lsarpc and srvsvc Transact pipes. This document is derived from NT Service Pack 1 and its corresponding version of Netmon. It is intended that an annotated packet trace be produced, which will likely be more instructive than this document.

Also needed, to fully implement NT Domain Login Services, is the document describing the cryptographic part of the NT authentication. This document is available from comp.protocols.smb; from the ntsecurity.net digest and from the samba digest, amongst other sources.

A copy is available from:

http://ntbugtraq.rc.on.ca/SCRIPTS/WA.EXE?A2=ind9708;L=ntbugtraq;O=A;P=2935

http://mailhost.cb1.com/~lkcl/crypt.html

A c-code implementation, provided by Linus Nordberg of this protocol is available from:

http://samba.org/cgi-bin/mfs/01/digest/1997/97aug/0391.html

http://mailhost.cb1.com/~lkcl/crypt.txt

Also used to provide debugging information is the Check Build version of NT workstation, and enabling full debugging in NETLOGON. This is achieved by setting the following REG_SZ registry key to 0x1ffffff:

HKLM\SYSTEM\CurrentControlSet\Services\Netlogon\Parameters

Incorrect direct editing of the registry can cause your machine to fail. Then again, so can incorrect implementation of this protocol. See "Liability:" above.

Bear in mind that each packet over-the-wire will have its origin in an API call. Therefore, there are likely to be structures, enumerations and defines that are usefully documented elsewhere.

This document is by no means complete or authoritative. Missing sections include, but are not limited to:

1. Mappings of RIDs to usernames (and vice-versa).

2. What a User ID is and what a Group ID is.

3. The exact meaning/definition of various magic constants or enumerations.

4. The reply error code and use of that error code when a workstation becomes a member of a domain (to be described later). Failure to return this error code will make the workstation report that it is already a member of the domain.

5. the cryptographic side of the NetrServerPasswordSet command, which would allow the workstation to change its password. This password is used to generate the long-term session key. [It is possible to reject this command, and keep the default workstation password].

9.2. Notes and Structures

        switch (switch_value)
        case 1:
        {
            ID_INFO_1     id_info_1;
        }

9.3. MSRPC over Transact Named Pipe

For details on the SMB Transact Named Pipe, see cifs6.txt

        initial SMBopenX request:         RPC API command 0x26 params:
        "\\PIPE\\lsarpc"                  0x65 0x63; 0x72 0x70; 0x44 0x65;
        "\\PIPE\\srvsvc"                  0x73 0x76; 0x4E 0x00; 0x5C 0x43;

abstract (0x4B324FC8, 0x01D31670, 0x475A7812, 0x88E16EBF, 0x00000003)
transfer (0x8A885D04, 0x11C91CEB, 0x0008E89F, 0x6048102B, 0x00000002)

switch (info class)
case 3:
case 5:
{
DOM_INFO domain info, levels 3 and 5 (are the same).
}

return    0 - indicates success

9.4. NETLOGON rpc Transact Named Pipe

The sequence of actions taken on this pipe are:

Defines for this pipe, identifying the query are

if (valid_user)
{
	UINT16      3 - switch value indicating USER_INFO structure.
    VOID*     non-zero - pointer to USER_INFO structure
    USER_INFO user logon information

    UINT32    1 - Authoritative response; 0 - Non-Auth?

    return    0 - indicates success
}
else
{
	UINT16    0 - switch value.  value to indicate no user presumed.
    VOID*     0x0000 0000 - indicates no USER_INFO structure.

    UINT32    1 - Authoritative response; 0 - Non-Auth?

    return    0xC000 0064 - NT_STATUS_NO_SUCH_USER.
}

9.5. \\MAILSLOT\NET\NTLOGON

Note: mailslots will contain a response mailslot, to which the response should be sent. the target NetBIOS name is REQUEST_NAME<20>, where REQUEST_NAME is the name of the machine that sent the request.

9.6. SRVSVC Transact Named Pipe

Defines for this pipe, identifying the query are:

9.7. Cryptographic side of NT Domain Authentication

9.8. SIDs and RIDs

SIDs and RIDs are well documented elsewhere.

A SID is an NT Security ID (see DOM_SID structure). They are of the form:

currently, the SID revision is 1. The Sub-Authorities are known as Relative IDs (RIDs).

10.1. Abstract

The purpose of this document is to provide some insight into Samba's printing functionality and also to describe the semantics of certain features of Windows client printing.

10.2. Printing Interface to Various Back ends

Samba uses a table of function pointers to seven functions. The function prototypes are defined in the printif structure declared in printing.h.

• retrieve the contents of a print queue

• pause the print queue

• resume a paused print queue

• delete a job from the queue

• pause a job in the print queue

• result a paused print job in the queue

• submit a job to the print queue

Currently there are only two printing back end implementations defined.

• a generic set of functions for working with standard UNIX printing subsystems

• a set of CUPS specific functions (this is only enabled if the CUPS libraries were located at compile time).

10.3. Print Queue TDB's

Samba provides periodic caching of the output from the "lpq command" for performance reasons. This cache time is configurable in seconds. Obviously the longer the cache time the less often smbd will be required to exec a copy of lpq. However, the accuracy of the print queue contents displayed to clients will be diminished as well.

The list of currently opened print queue TDB's can be found be examining the list of tdb_print_db structures ( see print_db_head in printing.c ). A queue TDB is opened using the wrapper function printing.c:get_print_db_byname(). The function ensures that smbd does not open more than MAX_PRINT_DBS_OPEN in an effort to prevent a large print server from exhausting all available file descriptors. If the number of open queue TDB's exceeds the MAX_PRINT_DBS_OPEN limit, smbd falls back to a most recently used algorithm for maintaining a list of open TDB's.

There are two ways in which a a print job can be entered into a print queue's TDB. The first is to submit the job from a Windows client which will insert the job information directly into the TDB. The second method is to have the print job picked up by executing the "lpq command".

/* included from printing.h */
struct printjob {
	pid_t pid; /* which process launched the job */
	int sysjob; /* the system (lp) job number */
	int fd; /* file descriptor of open file if open */
	time_t starttime; /* when the job started spooling */
	int status; /* the status of this job */
	size_t size; /* the size of the job so far */
	int page_count;	/* then number of pages so far */
	BOOL spooled; /* has it been sent to the spooler yet? */
	BOOL smbjob; /* set if the job is a SMB job */
	fstring filename; /* the filename used to spool the file */
	fstring jobname; /* the job name given to us by the client */
	fstring user; /* the user who started the job */
	fstring queuename; /* service number of printer for this job */
	NT_DEVICEMODE *nt_devmode;
};

The current manifestation of the printjob structure contains a field for the UNIX job id returned from the "lpq command" and a Windows job ID (32-bit bounded by PRINT_MAX_JOBID). When a print job is returned by the "lpq command" that does not match an existing job in the queue's TDB, a 32-bit job ID above the <*vance doesn't know what word is missing here*> is generating by adding UNIX_JOB_START to the id reported by lpq.

In order to match a 32-bit Windows jobid onto a 16-bit lanman print job id, smbd uses an in memory TDB to match the former to a number appropriate for old lanman clients.

When updating a print queue, smbd will perform the following steps ( refer to print.c:print_queue_update() ):

1. Check to see if another smbd is currently in the process of updating the queue contents by checking the pid stored in LOCK/printer_name. If so, then do not update the TDB.

2. Lock the mutex entry in the TDB and store our own pid. Check that this succeeded, else fail.

3. Store the updated time stamp for the new cache listing

4. Retrieve the queue listing via "lpq command"

5. 	foreach job in the queue
        	{
   		if the job is a UNIX job, create a new entry;
   		if the job has a Windows based jobid, then
   		{
   			Lookup the record by the jobid;
   			if the lookup failed, then
   				treat it as a UNIX job;
   			else
   				update the job status only
   		}
   	}

6. Delete any jobs in the TDB that are not in the in the lpq listing

7. Store the print queue status in the TDB

8. update the cache time stamp again

Note that it is the contents of this TDB that is returned to Windows clients and not the actual listing from the "lpq command".

The NT_DEVICEMODE stored as part of the printjob structure is used to store a pointer to a non-default DeviceMode associated with the print job. The pointer will be non-null when the client included a Device Mode in the OpenPrinterEx() call and subsequently submitted a job for printing on that same handle. If the client did not include a Device Mode in the OpenPrinterEx() request, the nt_devmode field is NULL and the job has the printer's device mode associated with it by default.

Only non-default Device Mode are stored with print jobs in the print queue TDB. Otherwise, the Device Mode is obtained from the printer object when the client issues a GetJob(level == 2) request.

10.4. ChangeID & Client Caching of Printer Information

[To be filled in later]

10.5. Windows NT/2K Printer Change Notify

When working with Windows NT+ clients, it is possible for a print server to use RPC to send asynchronous change notification events to clients for certain printer and print job attributes. This can be useful when the client needs to know that a new job has been added to the queue for a given printer or that the driver for a printer has been changed. Note that this is done entirely orthogonal to cache updates based on a new ChangeID for a printer object.

The basic set of RPC's used to implement change notification are

• RemoteFindFirstPrinterChangeNotifyEx ( RFFPCN )

• RemoteFindNextPrinterChangeNotifyEx ( RFNPCN )

• FindClosePrinterChangeNotify( FCPCN )

• ReplyOpenPrinter

• ReplyClosePrinter

• RouteRefreshPrinterChangeNotify ( RRPCN )

One additional RPC is available to a server, but is never used by the Windows spooler service:

• RouteReplyPrinter()

The opnum for all of these RPC's are defined in include/rpc_spoolss.h

Windows NT print servers use a bizarre method of sending print notification event to clients. The process of registering a new change notification handle is as follows. The 'C' is for client and the 'S' is for server. All error conditions have been eliminated.

C:	Obtain handle to printer or to the printer
	server via the standard OpenPrinterEx() call.
S:	Respond with a valid handle to object

C:	Send a RFFPCN request with the previously obtained
	handle with either (a) set of flags for change events
	to monitor, or (b) a PRINTER_NOTIFY_OPTIONS structure
	containing the event information to monitor.  The windows
	spooler has only been observed to use (b).
S:	The <* another missing word*> opens a new TCP session to the client (thus requiring
	all print clients to be CIFS servers as well) and sends
	a ReplyOpenPrinter() request to the client.
C:	The client responds with a printer handle that can be used to
	send event notification messages.
S:	The server replies success to the RFFPCN request.

C:	The windows spooler follows the RFFPCN with a RFNPCN
	request to fetch the current values of all monitored
	attributes.
S:	The server replies with an array SPOOL_NOTIFY_INFO_DATA
	structures (contained in a SPOOL_NOTIFY_INFO structure).

C:	If the change notification handle is ever released by the
	client via a FCPCN request, the server sends a ReplyClosePrinter()
	request back to the client first.  However a request of this
	nature from the client is often an indication that the previous
	notification event was not marshalled correctly by the server
	or a piece of data was wrong.
S:	The server closes the internal change notification handle
	(POLICY_HND) and does not send any further change notification
	events to the client for that printer or job.

The current list of notification events supported by Samba can be found by examining the internal tables in srv_spoolss_nt.c

• printer_notify_table[]

• job_notify_table[]

When an event occurs that could be monitored, smbd sends a message to itself about the change. The list of events to be transmitted are queued by the smbd process sending the message to prevent an overload of TDB usage and the internal message is sent during smbd's idle loop (refer to printing/notify.c and the functions send_spoolss_notify2_msg() and print_notify_send_messages() ).

The decision of whether or not the change is to be sent to connected clients is made by the routine which actually sends the notification. ( refer to srv_spoolss_nt.c:recieve_notify2_message() ).

Because it possible to receive a listing of multiple changes for multiple printers, the notification events must be split into categories by the printer name. This makes it possible to group multiple change events to be sent in a single RPC according to the printer handle obtained via a ReplyOpenPrinter().

The actual change notification is performed using the RRPCN request RPC. This packet contains

• the printer handle registered with the client's spooler on which the change occurred

• The change_low value which was sent as part of the last RFNPCN request from the client

• The SPOOL_NOTIFY_INFO container with the event information

A SPOOL_NOTIFY_INFO contains:

• the version and flags field are predefined and should not be changed

• The count field is the number of entries in the SPOOL_NOTIFY_INFO_DATA array

The SPOOL_NOTIFY_INFO_DATA entries contain:

• The type defines whether or not this event is for a printer or a print job

• The field is the flag identifying the event

• the notify_data union contains the new valuie of the attribute

• The enc_type defines the size of the structure for marshalling and unmarshalling

• (a) the id must be 0 for a printer event on a printer handle. (b) the id must be the job id for an event on a printer job (c) the id must be the matching number of the printer index used in the response packet to the RFNPCN when using a print server handle for notification. Samba currently uses the snum of the printer for this which can break if the list of services has been modified since the notification handle was registered.

• The size is either (a) the string length in UNICODE for strings, (b) the size in bytes of the security descriptor, or (c) 0 for data values.

11.1. WINS Failover

The current Samba codebase possesses the capability to use groups of WINS servers that share a common namespace for NetBIOS name registration and resolution. The formal parameter syntax is

	WINS_SERVER_PARAM 	= SERVER [ SEPARATOR SERVER_LIST ]
	WINS_SERVER_PARAM 	= "wins server"
	SERVER 			= ADDR[:TAG]
	ADDR 			= ip_addr | fqdn
	TAG 			= string
	SEPARATOR		= comma | \s+
	SERVER_LIST		= SERVER [ SEPARATOR SERVER_LIST ]

A simple example of a valid wins server setting is

[global]
	wins server = 192.168.1.2 192.168.1.3

In the event that no TAG is defined in for a SERVER in the list, smbd assigns a default TAG of "*". A TAG is used to group servers of a shared NetBIOS namespace together. Upon startup, nmbd will attempt to register the netbios name value with one server in each tagged group.

An example using tags to group WINS servers together is show here. Note that the use of interface names in the tags is only by convention and is not a technical requirement.

[global]
	wins server = 192.168.1.2:eth0 192.168.1.3:eth0 192.168.2.2:eth1

Using this configuration, nmbd would attempt to register the server's NetBIOS name with one WINS server in each group. Because the "eth0" group has two servers, the second server would only be used when a registration (or resolution) request to the first server in that group timed out.

NetBIOS name resolution follows a similar pattern as name registration. When resolving a NetBIOS name via WINS, smbd and other Samba programs will attempt to query a single WINS server in a tagged group until either a positive response is obtained at least once or until a server from every tagged group has responded negatively to the name query request. If a timeout occurs when querying a specific WINS server, that server is marked as down to prevent further timeouts and the next server in the WINS group is contacted. Once marked as dead, Samba will not attempt to contact that server for name registration/resolution queries for a period of 10 minutes.

12.1. Security in the 'new SAM'

One of the biggest problems with passdb is it's implementation of 'security'. Access control is on a 'are you root at the moment' basis, and it has no concept of NT ACLs. Things like ldapsam had to add 'magic' 'are you root' checks.

We took this very seriously when we started work, and the new structure is designed with this in mind, from the ground up. Each call to the SAM has a NT_TOKEN and (if relevant) an 'access desired'. This is either provided as a parameter, or implicitly supplied by the object being accessed.

For example, when you call

<
NTSTATUS sam_get_account_by_name(const SAM_CONTEXT *context, const
NT_USER_TOKEN *access_token, uint32 access_desired, const char *domain,
const char *name, SAM_ACCOUNT_HANDLE **account)

The context can be NULL (and is used to allow import/export by setting up 2 contexts, and allowing calls on both simultaneously)

The access token *must* be specified. Normally the user's token out of current_user, this can also be a global 'system' context.

The access desired is as per the ACL, for passing to the seaccess stuff.

The domain/username are standard. Even if we only have one domain, keeping this ensures that we don't get 'unqualified' usernames (same problem as we had with unqualified SIDs).

We return a 'handle'. This is opaque to the rest of Samba, but is operated on by get/set routines, all of which return NTSTATUS.

The access checking is done by the SAM module. The reason it is not done 'above' the interface is to ensure a 'choke point'. I put a lot of effort into the auth subsystem to ensure we never 'accidentally' forgot to check for null passwords, missed a restriction etc. I intend the SAM to be written with the same caution.

The reason the access checking is not handled by the interface itself is due to the different implementations it make take on. For example, on ADS, you cannot set a password over a non-SSL connection. Other backends may have similar requirements - we need to leave this policy up to the modules. They will naturally have access to 'helper' procedures and good examples to avoid mishaps.

(Furthermore, some backends my actually chose to push the whole ACL issue to the remote server, and - assuming ldap for this example - bind as the user directly)

Each returned handle has an internal 'access permitted', which allows the 'get' and 'set' routines to return 'ACCESS_DENIED' for things that were not able to be retrieved from the backend. This removes the need to specify the NT_TOKEN on every operation, and allows for 'object not present' to be easily distinguished from 'access denied'.

When you 'set' an object (calling sam_update_account) the internal details are again used. Each change that has been made to the object has been flagged, so as to avoid race conditions (on unmodified components) and to avoid violating any extra ACL requirements on the actual data store (like the LDAP server).

Finally, we have generic get_sec_desc() and set_sec_desc() routines to allow external ACL manipulation. These do lookups based on SID.

12.2. Standalone from UNIX

One of the primary tenants of the 'new SAM' is that it would not attempt to deal with 'what unix id for that'. This would be left to the 'SMS' (Sid Mapping System') or SID farm, and probably administered via winbind. We have had constructive discussion on how 'basic' unix accounts like 'root' would be handled, and we think this can work. Accounts not preexisting in unix would be served up via winbind.

This is an *optional* part, and my preferred end-game. We have a fare way to go before things like winbind up to it however.

12.3. Handles and Races in the new SAM

One of the things that the 'new SAM' work has tried to face is both compatibility with existing code, and a closer alignment to the SAMR interface. I consider SAMR to be a 'primary customer' to the this work, because if we get alignment with that wrong, things get more, rather than less complex. Also, most other parts of Samba are much more flexible with what they can allow.

In any case, that was a decision taken as to how the general design would progress. BTW, my understanding of SAMR may be completely flawed.

One of the most race-prone areas of the new code is the conflicting update problem. We have taken two approaches:

• 'Not conflicting' conflicts. Due to the way usrmgr operates, it will open a user, display all the properties and *save* them all, even if you don't change any.

  For this, see what I've done in rpc_server/srv_samr_util.c. I intend to take this one step further, and operate on the 'handle' that the values were read from. This should mean that we only update things that have *really* changed.

• 'conflicting' updates: Currently we don't deal with this (in passdb or the new sam stuff), but the design is sufficiently flexible to 'deny' a second update. I don't foresee locking records however.

12.4. Layers

12.5. SAM Modules

12.6. Memory Management

The 'new SAM' development effort also concerned itself with getting a sane implementation of memory management. It was decided that we would be (as much as possible) talloc based, using an 'internal talloc context' on many objects. That is, the creation of an object would initiate it's own internal talloc context, and this would be used for all operations on that object. Much of this is already implemented in passdb. Also, like passdb, it will be possible to specify that some object actually be created on a specified context.

Memory management is important here because the APIs in the 'new SAM' do not use 'pdb_init()' or an equivalent. They always allocate new objects. Enumeration's are slightly different, and occur on a supplied context that 'owns' the entire list, rather than per-element. (the enumeration functions return an array of all elements - not full handles just basic (and public) info) Likewise for things that fill in a char **.

For example:

NTSTATUS sam_lookup_sid(const SAM_CONTEXT *context, const NT_USER_TOKEN
*access_token, TALLOC_CTX *mem_ctx, const DOM_SID *sid, char **name,
uint32 *type)

Takes a context to allocate the 'name' on, while:

NTSTATUS sam_get_account_by_sid(const SAM_CONTEXT *context, const
NT_USER_TOKEN *access_token, uint32 access_desired, const DOM_SID
*accountsid, SAM_ACCOUNT_HANDLE **account)

Allocates a handle and stores the allocation context on that handle.

I think that the following:

NTSTATUS sam_enum_accounts(const SAM_CONTEXT *context, const
NT_USER_TOKEN *access_token, const DOM_SID *domainsid, uint16 acct_ctrl,
int32 *account_count, SAM_ACCOUNT_ENUM **accounts)

12.7. Testing

Testing is vital in any piece of software, and Samba is certainly no exception. In designing this new subsystem, we have taken care to ensure it is easily tested, independent of outside protocols.

To this end, Jelmer has constructed 'samtest'.

This utility (see torture/samtest.c) is structured like rpcclient, but instead operates on the SAM subsystem. It creates a 'custom' SAM context, that may be distinct from the default values used by the rest of the system, and can load a separate configuration file.

A small number of commands are currently implemented, but these have already proved vital in testing. I expect SAM module authors will find it particularly valuable.

Example useage:

$ bin/samtest

> context ads:ldap://192.168.1.96

> lookup_name DOMAIN abartlet

Because the 'new SAM' is NT ACL based, there will be a command to specify an arbitrary NT ACL, but for now it uses 'system' by default.

13.1. Introduction

With the development of LanManager and Windows NT compatible password encryption for Samba, it is now able to validate user connections in exactly the same way as a LanManager or Windows NT server.

This document describes how the SMB password encryption algorithm works and what issues there are in choosing whether you want to use it. You should read it carefully, especially the part about security and the "PROS and CONS" section.

13.2. How does it work?

LanManager encryption is somewhat similar to UNIX password encryption. The server uses a file containing a hashed value of a user's password. This is created by taking the user's plaintext password, capitalising it, and either truncating to 14 bytes or padding to 14 bytes with null bytes. This 14 byte value is used as two 56 bit DES keys to encrypt a 'magic' eight byte value, forming a 16 byte value which is stored by the server and client. Let this value be known as the "hashed password".

Windows NT encryption is a higher quality mechanism, consisting of doing an MD4 hash on a Unicode version of the user's password. This also produces a 16 byte hash value that is non-reversible.

When a client (LanManager, Windows for WorkGroups, Windows 95 or Windows NT) wishes to mount a Samba drive (or use a Samba resource), it first requests a connection and negotiates the protocol that the client and server will use. In the reply to this request the Samba server generates and appends an 8 byte, random value - this is stored in the Samba server after the reply is sent and is known as the "challenge". The challenge is different for every client connection.

The client then uses the hashed password (16 byte values described above), appended with 5 null bytes, as three 56 bit DES keys, each of which is used to encrypt the challenge 8 byte value, forming a 24 byte value known as the "response".

In the SMB call SMBsessionsetupX (when user level security is selected) or the call SMBtconX (when share level security is selected), the 24 byte response is returned by the client to the Samba server. For Windows NT protocol levels the above calculation is done on both hashes of the user's password and both responses are returned in the SMB call, giving two 24 byte values.

The Samba server then reproduces the above calculation, using its own stored value of the 16 byte hashed password (read from the smbpasswd file - described later) and the challenge value that it kept from the negotiate protocol reply. It then checks to see if the 24 byte value it calculates matches the 24 byte value returned to it from the client.

If these values match exactly, then the client knew the correct password (or the 16 byte hashed value - see security note below) and is thus allowed access. If not, then the client did not know the correct password and is denied access.

Note that the Samba server never knows or stores the cleartext of the user's password - just the 16 byte hashed values derived from it. Also note that the cleartext password or 16 byte hashed values are never transmitted over the network - thus increasing security.

13.3. The smbpasswd file

In order for Samba to participate in the above protocol it must be able to look up the 16 byte hashed values given a user name. Unfortunately, as the UNIX password value is also a one way hash function (ie. it is impossible to retrieve the cleartext of the user's password given the UNIX hash of it), a separate password file containing this 16 byte value must be kept. To minimise problems with these two password files, getting out of sync, the UNIX /etc/passwd and the smbpasswd file, a utility, mksmbpasswd.sh, is provided to generate a smbpasswd file from a UNIX /etc/passwd file.

To generate the smbpasswd file from your /etc/passwd file use the following command :

$ cat /etc/passwd | mksmbpasswd.sh > /usr/local/samba/private/smbpasswd

If you are running on a system that uses NIS, use

$ ypcat passwd | mksmbpasswd.sh > /usr/local/samba/private/smbpasswd

The mksmbpasswd.sh program is found in the Samba source directory. By default, the smbpasswd file is stored in :

/usr/local/samba/private/smbpasswd

The owner of the /usr/local/samba/private/ directory should be set to root, and the permissions on it should be set to 0500 (chmod 500 /usr/local/samba/private).

Likewise, the smbpasswd file inside the private directory should be owned by root and the permissions on is should be set to 0600 (chmod 600 smbpasswd).

The format of the smbpasswd file is (The line has been wrapped here. It should appear as one entry per line in your smbpasswd file.)

username:uid:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX:
	[Account type]:LCT-<last-change-time>:Long name
	

Although only the username, uid, XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX, [Account type] and last-change-time sections are significant and are looked at in the Samba code.

It is VITALLY important that there by 32 'X' characters between the two ':' characters in the XXX sections - the smbpasswd and Samba code will fail to validate any entries that do not have 32 characters between ':' characters. The first XXX section is for the Lanman password hash, the second is for the Windows NT version.

When the password file is created all users have password entries consisting of 32 'X' characters. By default this disallows any access as this user. When a user has a password set, the 'X' characters change to 32 ascii hexadecimal digits (0-9, A-F). These are an ascii representation of the 16 byte hashed value of a user's password.

To set a user to have no password (not recommended), edit the file using vi, and replace the first 11 characters with the ascii text "NO PASSWORD" (minus the quotes).

For example, to clear the password for user bob, his smbpasswd file entry would look like :

	bob:100:NO PASSWORDXXXXXXXXXXXXXXXXXXXXX:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX:[U          ]:LCT-00000000:Bob's full name:/bobhome:/bobshell
	

If you are allowing users to use the smbpasswd command to set their own passwords, you may want to give users NO PASSWORD initially so they do not have to enter a previous password when changing to their new password (not recommended). In order for you to allow this the smbpasswd program must be able to connect to the smbd daemon as that user with no password. Enable this by adding the line :

null passwords = yes

to the [global] section of the smb.conf file (this is why the above scenario is not recommended). Preferably, allocate your users a default password to begin with, so you do not have to enable this on your server.

Note : This file should be protected very carefully. Anyone with access to this file can (with enough knowledge of the protocols) gain access to your SMB server. The file is thus more sensitive than a normal unix /etc/passwd file.