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diff --git a/docs/docbook/devdoc/sam.xml b/docs/docbook/devdoc/sam.xml new file mode 100644 index 0000000000..84c17d65e2 --- /dev/null +++ b/docs/docbook/devdoc/sam.xml @@ -0,0 +1,357 @@ +<chapter id="sam"> + +<chapterinfo> + <author> + <firstname>Andrew</firstname><surname>Bartlett</surname> + </author> + <pubdate>1 October 2002</pubdate> +</chapterinfo> + +<title>The Upcoming SAM System</title> + +<sect1> +<title>Security in the 'new SAM'</title> + +<para>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.</para> + +<para>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.</para> + +<para> +For example, when you call +</para> + +<programlisting> +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) +</programlisting> + +<para> +The context can be NULL (and is used to allow import/export by setting +up 2 contexts, and allowing calls on both simultaneously) +</para> + +<para> +The access token *must* be specified. Normally the user's token out of +current_user, this can also be a global 'system' context. +</para> + +<para> +The access desired is as per the ACL, for passing to the seaccess stuff. +</para> + +<para> +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). +</para> + +<para> +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. +</para> + +<para> +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. +</para> + +<para> +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. +</para> + +<para> +(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) +</para> + +<para> +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'. +</para> + +<para> +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). +</para> + +<para> +Finally, we have generic get_sec_desc() and set_sec_desc() routines to +allow external ACL manipulation. These do lookups based on SID. +</para> + +</sect1> + +<sect1> +<title>Standalone from UNIX</title> + +<para> +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. +</para> + +<para> +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. +</para> + +</sect1> + +<sect1> +<title>Handles and Races in the new SAM</title> + +<para> +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. +</para> + +<para> +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. +</para> + +<para> +One of the most race-prone areas of the new code is the conflicting +update problem. We have taken two approaches: +</para> + +<itemizedlist> +<listitem> +<para>'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. +</para> + +<para> +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. +</para> +</listitem> + +<listitem> +<para> +'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. +</para> +</listitem> +</itemizedlist> + +</sect1> + +<sect1> +<title>Layers</title> + +<sect2> +<title>Application</title> + +<para> +This is where smbd, samtest and whatever end-user replacement we have +for pdbedit sits. They use only the SAM interface, and do not get +'special knowledge' of what is below them. +</para> +</sect2> +<sect2> +<title>SAM Interface</title> + +<para> +This level 'owns' the various handle structures, the get/set routines on +those structures and provides the public interface. The application +layer may initialize a 'context' to be passed to all interface routines, +else a default, self-initialising context will be supplied. This layser +finds the appropriate backend module for the task, and tries very hard +not to need to much 'knowledge'. It should just provide the required +abstraction to the modules below, and arrange for their initial loading. +</para> + +<para> +We could possibly add ACL checking at this layer, to avoid discrepancies +in implementation modules. +</para> + +</sect2> + +<sect2> +<title>SAM Modules</title> + +<para> +These do not communicate with the application directly, only by setting +values in the handles, and receiving requests from the interface. These +modules are responsible for translating values from the handle's +.private into (say) an LDAP modification list. The module is expected +to 'know' things like it's own domain SID, domain name, and any other +state attached to the SAM. Simpler modules may call back to some helper +routine. +</para> + +</sect2> +</sect1> + +<sect1> +<title>SAM Modules</title> + +<sect2> +<title>Special Module: sam_passdb</title> + +<para> +In order for there to be a smooth transition, kai is writing a module +that reads existing passdb backends, and translates them into SAM +replies. (Also pulling data from the account policy DB etc). We also +intend to write a module that does the reverse - gives the SAM a passdb +interface. +</para> +</sect2> + +<sect2> +<title>sam_ads</title> +<para> +This is the first of the SAM modules to be committed to the tree - +mainly because I needed to coordinate work with metze (who authored most +of it). This module aims to use Samba's libads code to provide an +Active Directory LDAP client, suitable for use on a mixed-mode DC. +While it is currently being tested against Win2k servers (with a +password in the smb.conf file) it is expected to eventually use a +(possibly modified) OpenLDAP server. We hope that this will assist in +the construction of an Samba AD DC. +</para> + +<para> +We also intend to construct a Samba 2.2/3.0 compatible ldap module, +again using libads code. +</para> +</sect2> +</sect1> + +<sect1> +<title>Memory Management</title> + +<para> +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. +</para> + +<para> +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 +**. +</para> + +<para>For example:</para> + +<para><programlisting> +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) +</programlisting></para> + +<para>Takes a context to allocate the 'name' on, while:</para> + +<para><programlisting> +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) +</programlisting></para> + +<para>Allocates a handle and stores the allocation context on that handle.</para> + +<para>I think that the following:</para> + +<para><programlisting> +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) +</programlisting></para> + +</sect1> + +<sect1> +<title>Testing</title> + +<para> +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. +</para> + +<para> +To this end, Jelmer has constructed 'samtest'. +</para> + +<para> +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. +</para> + +<para> +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. +</para> + +<para>Example useage:</para> + +<para><prompt>$</prompt> <command>bin/samtest</command></para> + +<para><programlisting> +> context ads:ldap://192.168.1.96 +</programlisting> +(this loads a new context, using the new ADS module. The parameter is +the 'location' of the ldap server) +</para> + +<para><programlisting> +> lookup_name DOMAIN abartlet +</programlisting> +(returns a sid). +</para> + +<para> +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. +</para> +</sect1> +</chapter> |