I've been working on refactoring some of the mess that is the become_user()

code.  This code is now implemented as a stack of security contexts, where
a security context is defined as a set of effective user, group and
supplementary group ids.

The following functions are implemented:

BOOL push_sec_ctx(void);

     Create a new security context on the stack which is the same as the
     current security context.

void set_sec_ctx(uid_t uid, gid_t gid, int ngroups, gid_t *groups);

     Set the current security context to a given set of user and group
     ids.

void set_root_sec_ctx(void);

     Set to uid = gid = 0.  No supplementary groups are set.

BOOL pop_sec_ctx(void);

     Pop a security context from the stack and restore the user and group
     permissions of the previous context.

void init_sec_ctx(void);

     Initialise the security context stack.  This must be called before any
     of the other operations are used or weird things may happen.

The idea is that there is a base security context which is either root or
some authenticated unix user.  Other security contexts can be pushed and
popped as needed for things like changing passwords, or rpc pipe operations
where the rpc pipe user is different from the smb user.
(This used to be commit 87c78d6d5a6bf8d0907d6f8ef5ee0d642946cad3)

1 files changed, 295 insertions, 0 deletions

diff --git a/source3/smbd/sec_ctx.c b/source3/smbd/sec_ctx.c
new file mode 100644
index 0000000000..e3aac77d8e
--- /dev/null
+++ b/source3/smbd/sec_ctx.c
@@ -0,0 +1,295 @@
+/* 
+   Unix SMB/Netbios implementation.
+   Version 1.9.
+   uid/user handling
+   Copyright (C) Tim Potter 2000
+   
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 2 of the License, or
+   (at your option) any later version.
+   
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+   
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+*/
+
+#include "includes.h"
+
+extern int DEBUGLEVEL;
+extern struct current_user current_user;
+
+struct sec_ctx {
+	uid_t uid;
+	uid_t gid;
+	int ngroups;
+	gid_t *groups;
+};
+
+/* A stack of security contexts.  We include the current context as being
+   the first one, so there is room for another MAX_SEC_CTX_DEPTH more. */
+
+static struct sec_ctx sec_ctx_stack[MAX_SEC_CTX_DEPTH + 1];
+static int sec_ctx_stack_ndx;
+
+/* Become the specified uid */
+
+static BOOL become_uid(uid_t uid)
+{
+	/* Check for dodgy uid values */
+
+	if (uid == (uid_t)-1 || 
+	    ((sizeof(uid_t) == 2) && (uid == (uid_t)65535))) {
+		static int done;
+ 
+		if (!done) {
+			DEBUG(1,("WARNING: using uid %d is a security risk\n",
+				 (int)uid));
+			done = 1;
+		}
+	}
+
+	/* Set effective user id */
+
+	set_effective_uid(uid);
+	current_user.uid = uid;
+
+#ifdef WITH_PROFILE
+	profile_p->uid_changes++;
+#endif
+
+	return True;
+}
+
+/* Become the specified gid */
+
+static BOOL become_gid(gid_t gid)
+{
+	/* Check for dodgy gid values */
+
+	if (gid == (gid_t)-1 || ((sizeof(gid_t) == 2) && 
+				 (gid == (gid_t)65535))) {
+		static int done;
+		
+		if (!done) {
+			DEBUG(1,("WARNING: using gid %d is a security risk\n",
+				 (int)gid));  
+			done = 1;
+		}
+	}
+  
+	/* Set effective group id */
+
+	set_effective_gid(gid);
+	current_user.gid = gid;
+	
+	return True;
+}
+
+/* Become the specified uid and gid */
+
+static BOOL become_id(uid_t uid, gid_t gid)
+{
+	return become_gid(gid) && become_uid(uid);
+}
+
+/* Drop back to root privileges in order to change to another user */
+
+static void gain_root(void)
+{
+	if (geteuid() != 0) {
+		set_effective_uid(0);
+
+		if (geteuid() != 0) {
+			DEBUG(0,
+			      ("Warning: You appear to have a trapdoor "
+			       "uid system\n"));
+		}
+	}
+
+	if (getegid() != 0) {
+		set_effective_gid(0);
+
+		if (getegid() != 0) {
+			DEBUG(0,
+			      ("Warning: You appear to have a trapdoor "
+			       "gid system\n"));
+		}
+	}
+}
+
+/* Get the list of current groups */
+
+static void get_current_groups(int *ngroups, gid_t **groups)
+{
+	*ngroups = getgroups(0, NULL);
+	*groups = (gid_t *)malloc(*ngroups * sizeof(gid_t));
+
+	if (!groups) {
+		DEBUG(0, ("Out of memory in get_current_groups\n"));
+		return;
+	}
+
+	getgroups(*ngroups, *groups);
+}
+
+/* Create a new security context on the stack.  It is the same as the old
+   one.  User changes are done using the set_sec_ctx() function. */
+
+BOOL push_sec_ctx(void)
+{
+	/* Check we don't overflow our stack */
+
+	if (sec_ctx_stack_ndx == (MAX_SEC_CTX_DEPTH)) {
+		DEBUG(0, ("Security context stack overflow!\n"));
+		return False;
+	}
+
+	/* Store previous user context */
+
+	sec_ctx_stack_ndx++;
+
+	sec_ctx_stack[sec_ctx_stack_ndx].uid = geteuid();
+	sec_ctx_stack[sec_ctx_stack_ndx].gid = getegid();
+
+	sec_ctx_stack[sec_ctx_stack_ndx].ngroups = sys_getgroups(0, NULL);
+
+	if (!(sec_ctx_stack[sec_ctx_stack_ndx].groups = 
+	      malloc(sec_ctx_stack[sec_ctx_stack_ndx].ngroups * 
+		     sizeof(gid_t)))) {
+		DEBUG(0, ("Out of memory in push_sec_ctx()\n"));
+		return False;
+	}
+
+	sys_getgroups(sec_ctx_stack[sec_ctx_stack_ndx].ngroups,
+		  sec_ctx_stack[sec_ctx_stack_ndx].groups);
+
+	return True;
+}
+
+/* Set the current security context to a given user */
+
+void set_sec_ctx(uid_t uid, gid_t gid, int ngroups, gid_t *groups)
+{
+	/* Set the security context */
+
+	DEBUG(3, ("setting sec ctx (%d, %d)\n", uid, gid));
+
+	gain_root();
+
+#ifdef HAVE_SETGROUPS
+	sys_setgroups(ngroups, groups);
+
+	sec_ctx_stack[sec_ctx_stack_ndx].ngroups = ngroups;
+	sec_ctx_stack[sec_ctx_stack_ndx].groups = 
+		memdup(groups, sizeof(gid_t) * ngroups);
+#endif
+
+	become_id(uid, gid);
+
+	sec_ctx_stack[sec_ctx_stack_ndx].uid = uid;
+	sec_ctx_stack[sec_ctx_stack_ndx].gid = gid;
+
+	/* Update current_user stuff */
+
+	current_user.uid = uid;
+	current_user.gid = gid;
+	current_user.ngroups = ngroups;
+	current_user.groups = groups;
+}
+
+/* Become root context */
+
+void set_root_sec_ctx(void)
+{
+	/* May need to worry about supplementary groups at some stage */
+
+	set_sec_ctx(0, 0, 0, NULL);
+}
+
+/* Pop a security context from the stack */
+
+BOOL pop_sec_ctx(void)
+{
+	/* Check for stack underflow */
+
+	if (sec_ctx_stack_ndx == 0) {
+		DEBUG(0, ("Security context stack underflow!\n"));
+		return False;
+	}
+
+	/* Clear previous user info */
+
+	sec_ctx_stack[sec_ctx_stack_ndx].uid = (uid_t)-1;
+	sec_ctx_stack[sec_ctx_stack_ndx].gid = (gid_t)-1;
+
+	safe_free(sec_ctx_stack[sec_ctx_stack_ndx].groups);
+	sec_ctx_stack[sec_ctx_stack_ndx].ngroups = 0;
+
+	/* Pop back previous user */
+
+	sec_ctx_stack_ndx--;
+
+	gain_root();
+
+#ifdef HAVE_SETGROUPS
+	sys_setgroups(sec_ctx_stack[sec_ctx_stack_ndx].ngroups,
+		      sec_ctx_stack[sec_ctx_stack_ndx].groups);
+#endif
+
+	become_id(sec_ctx_stack[sec_ctx_stack_ndx].uid,
+		  sec_ctx_stack[sec_ctx_stack_ndx].gid);
+
+	/* Update current_user stuff */
+
+	current_user.uid = sec_ctx_stack[sec_ctx_stack_ndx].uid;
+	current_user.gid = sec_ctx_stack[sec_ctx_stack_ndx].gid;
+	current_user.ngroups = sec_ctx_stack[sec_ctx_stack_ndx].ngroups;
+	current_user.groups = sec_ctx_stack[sec_ctx_stack_ndx].groups;
+
+	DEBUG(3, ("popped off to sec ctx (%d, %d)\n", geteuid(), getegid()));
+
+	return True;
+}
+
+/* Initialise the security context system */
+
+void init_sec_ctx(void)
+{
+	int i;
+
+	/* Initialise security context stack */
+
+	memset(sec_ctx_stack, 0, sizeof(struct sec_ctx) * MAX_SEC_CTX_DEPTH);
+
+	for (i = 0; i < MAX_SEC_CTX_DEPTH; i++) {
+		sec_ctx_stack[i].uid = (uid_t)-1;
+		sec_ctx_stack[i].gid = (gid_t)-1;
+	}
+
+	/* Initialise first level of stack.  It is the current context */
+
+	sec_ctx_stack[0].uid = geteuid();
+	sec_ctx_stack[0].gid = getegid();
+
+	get_current_groups(&sec_ctx_stack[0].ngroups,
+			   &sec_ctx_stack[0].groups);
+
+	/* Initialise current_user global */
+
+	current_user.uid = sec_ctx_stack[sec_ctx_stack_ndx].uid;
+	current_user.gid = sec_ctx_stack[sec_ctx_stack_ndx].gid;
+	current_user.ngroups = sec_ctx_stack[sec_ctx_stack_ndx].ngroups;
+	current_user.groups = sec_ctx_stack[sec_ctx_stack_ndx].groups;
+
+	/* The conn and vuid are usually taken care of by other modules.
+	   We initialise them here. */
+
+	current_user.conn = NULL;
+	current_user.vuid = UID_FIELD_INVALID;
+}