sec_ctx.c

/* 
   Unix SMB/CIFS implementation.
   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 3 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, see <http://www.gnu.org/licenses/>.
*/

#include "includes.h"
#include "system/passwd.h"
#include "smbd/smbd.h"
#include "smbd/globals.h"
#include "libcli/security/security_token.h"
#include "auth.h"
#include "smbprofile.h"
#include "../lib/util/setid.h"

extern struct current_user current_user;

/****************************************************************************
 Are two UNIX tokens equal ?
****************************************************************************/

bool unix_token_equal(const struct security_unix_token *t1, const struct security_unix_token *t2)
{
	if (t1->uid != t2->uid || t1->gid != t2->gid ||
			t1->ngroups != t2->ngroups) {
		return false;
	}
	if (memcmp(t1->groups, t2->groups,
			t1->ngroups*sizeof(gid_t)) != 0) {
		return false;
	}
	return true;
}

/****************************************************************************
 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))) {
		if (!become_uid_done) {
			DEBUG(1,("WARNING: using uid %d is a security risk\n",
				 (int)uid));
			become_uid_done = true;
		}
	}

	/* Set effective user id */

	set_effective_uid(uid);

	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))) {
		if (!become_gid_done) {
			DEBUG(1,("WARNING: using gid %d is a security risk\n",
				 (int)gid));  
			become_gid_done = true;
		}
	}

	/* Set effective group id */

	set_effective_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 (non_root_mode()) {
		return;
	}

	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 int get_current_groups(gid_t gid, uint32_t *p_ngroups, gid_t **p_groups)
{
	int i;
	int ngroups;
	gid_t *groups = NULL;

	(*p_ngroups) = 0;
	(*p_groups) = NULL;

	/* this looks a little strange, but is needed to cope with
	   systems that put the current egid in the group list
	   returned from getgroups() (tridge) */
	save_re_gid();
	set_effective_gid(gid);
	samba_setgid(gid);

	ngroups = sys_getgroups(0, NULL);
	if (ngroups <= 0) {
		goto fail;
	}

	if((groups = SMB_MALLOC_ARRAY(gid_t, ngroups+1)) == NULL) {
		DEBUG(0,("setup_groups malloc fail !\n"));
		goto fail;
	}

	if ((ngroups = sys_getgroups(ngroups,groups)) == -1) {
		goto fail;
	}

	restore_re_gid();

	(*p_ngroups) = ngroups;
	(*p_groups) = groups;

	DEBUG( 4, ( "get_current_groups: user is in %u groups: ", ngroups));
	for (i = 0; i < ngroups; i++ ) {
		DEBUG( 4, ( "%s%d", (i ? ", " : ""), (int)groups[i] ) );
	}
	DEBUG( 4, ( "\n" ) );

	return ngroups;

fail:
	SAFE_FREE(groups);
	restore_re_gid();
	return -1;
}

/****************************************************************************
 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)
{
	struct sec_ctx *ctx_p;

	START_PROFILE(push_sec_ctx);

	/* Check we don't overflow our stack */

	if (sec_ctx_stack_ndx == MAX_SEC_CTX_DEPTH) {
		DEBUG(0, ("Security context stack overflow!\n"));
		smb_panic("Security context stack overflow!");
	}

	/* Store previous user context */

	sec_ctx_stack_ndx++;

	ctx_p = &sec_ctx_stack[sec_ctx_stack_ndx];

	ctx_p->ut.uid = geteuid();
	ctx_p->ut.gid = getegid();

 	DEBUG(4, ("push_sec_ctx(%u, %u) : sec_ctx_stack_ndx = %d\n", 
 		  (unsigned int)ctx_p->ut.uid, (unsigned int)ctx_p->ut.gid, sec_ctx_stack_ndx ));

	ctx_p->token = dup_nt_token(NULL,
				    sec_ctx_stack[sec_ctx_stack_ndx-1].token);

	ctx_p->ut.ngroups = sys_getgroups(0, NULL);

	if (ctx_p->ut.ngroups != 0) {
		if (!(ctx_p->ut.groups = SMB_MALLOC_ARRAY(gid_t, ctx_p->ut.ngroups))) {
			DEBUG(0, ("Out of memory in push_sec_ctx()\n"));
			TALLOC_FREE(ctx_p->token);
			return False;
		}

		sys_getgroups(ctx_p->ut.ngroups, ctx_p->ut.groups);
	} else {
		ctx_p->ut.groups = NULL;
	}

	END_PROFILE(push_sec_ctx);

	return True;
}

/****************************************************************************
 Change UNIX security context. Calls panic if not successful so no return value.
****************************************************************************/

#ifndef HAVE_DARWIN_INITGROUPS

/* Normal credential switch path. */

static void set_unix_security_ctx(uid_t uid, gid_t gid, int ngroups, gid_t *groups)
{
	/* Start context switch */
	gain_root();
#ifdef HAVE_SETGROUPS
	if (sys_setgroups(gid, ngroups, groups) != 0 && !non_root_mode()) {
		smb_panic("sys_setgroups failed");
	}
#endif
	become_id(uid, gid);
	/* end context switch */
}

#else /* HAVE_DARWIN_INITGROUPS */

/* The Darwin groups implementation is a little unusual. The list of
* groups in the kernel credential is not exhaustive, but more like
* a cache. The full group list is held in userspace and checked
* dynamically.
*
* This is an optional mechanism, and setgroups(2) opts out
* of it. That is, if you call setgroups, then the list of groups you
* set are the only groups that are ever checked. This is not what we
* want. We want to opt in to the dynamic resolution mechanism, so we
* need to specify the uid of the user whose group list (cache) we are
* setting.
*
* The Darwin rules are:
*  1. Thou shalt setegid, initgroups and seteuid IN THAT ORDER
*  2. Thou shalt not pass more that NGROUPS_MAX to initgroups
*  3. Thou shalt leave the first entry in the groups list well alone
*/

#include <sys/syscall.h>

static void set_unix_security_ctx(uid_t uid, gid_t gid, int ngroups, gid_t *groups)
{
	int max = groups_max();

	/* Start context switch */
	gain_root();

	become_gid(gid);


	if (syscall(SYS_initgroups, (ngroups > max) ? max : ngroups,
			groups, uid) == -1 && !non_root_mode()) {
		DEBUG(0, ("WARNING: failed to set group list "
			"(%d groups) for UID %d: %s\n",
			ngroups, uid, strerror(errno)));
		smb_panic("sys_setgroups failed");
	}

	become_uid(uid);
	/* end context switch */
}

#endif /* HAVE_DARWIN_INITGROUPS */

/****************************************************************************
 Set the current security context to a given user.
****************************************************************************/

static void set_sec_ctx_internal(uid_t uid, gid_t gid,
				 int ngroups, gid_t *groups,
				 const struct security_token *token)
{
	struct sec_ctx *ctx_p = &sec_ctx_stack[sec_ctx_stack_ndx];

	/* Set the security context */

	DEBUG(4, ("setting sec ctx (%u, %u) - sec_ctx_stack_ndx = %d\n", 
		(unsigned int)uid, (unsigned int)gid, sec_ctx_stack_ndx));

	security_token_debug(DBGC_CLASS, 5, token);
	debug_unix_user_token(DBGC_CLASS, 5, uid, gid, ngroups, groups);

	/* Change uid, gid and supplementary group list. */
	set_unix_security_ctx(uid, gid, ngroups, groups);

	ctx_p->ut.ngroups = ngroups;

	SAFE_FREE(ctx_p->ut.groups);
	if (token && (token == ctx_p->token)) {
		smb_panic("DUPLICATE_TOKEN");
	}

	TALLOC_FREE(ctx_p->token);

	if (ngroups) {
		ctx_p->ut.groups = (gid_t *)smb_xmemdup(groups,
						        sizeof(gid_t) * ngroups);
	} else {
		ctx_p->ut.groups = NULL;
	}

	if (token) {
		ctx_p->token = dup_nt_token(NULL, token);
		if (!ctx_p->token) {
			smb_panic("dup_nt_token failed");
		}
	} else {
		ctx_p->token = NULL;
	}

	ctx_p->ut.uid = uid;
	ctx_p->ut.gid = gid;

	/* Update current_user stuff */

	current_user.ut.uid = uid;
	current_user.ut.gid = gid;
	current_user.ut.ngroups = ngroups;
	current_user.ut.groups = groups;
	current_user.nt_user_token = ctx_p->token;
}

void set_sec_ctx(uid_t uid, gid_t gid, int ngroups, gid_t *groups, const struct security_token *token)
{
	START_PROFILE(set_sec_ctx);
	set_sec_ctx_internal(uid, gid, ngroups, groups, token);
	END_PROFILE(set_sec_ctx);
}

/****************************************************************************
 Become root context.
****************************************************************************/

void set_root_sec_ctx(void)
{
	/* May need to worry about supplementary groups at some stage */

	START_PROFILE(set_root_sec_ctx);
	set_sec_ctx_internal(0, 0, 0, NULL, NULL);
	END_PROFILE(set_root_sec_ctx);
}

/****************************************************************************
 Pop a security context from the stack.
****************************************************************************/

bool pop_sec_ctx(void)
{
	struct sec_ctx *ctx_p;
	struct sec_ctx *prev_ctx_p;

	START_PROFILE(pop_sec_ctx);

	/* Check for stack underflow */

	if (sec_ctx_stack_ndx == 0) {
		DEBUG(0, ("Security context stack underflow!\n"));
		smb_panic("Security context stack underflow!");
	}

	ctx_p = &sec_ctx_stack[sec_ctx_stack_ndx];

	/* Clear previous user info */

	ctx_p->ut.uid = (uid_t)-1;
	ctx_p->ut.gid = (gid_t)-1;

	SAFE_FREE(ctx_p->ut.groups);
	ctx_p->ut.ngroups = 0;

	TALLOC_FREE(ctx_p->token);

	/* Pop back previous user */

	sec_ctx_stack_ndx--;

	prev_ctx_p = &sec_ctx_stack[sec_ctx_stack_ndx];

	/* Change uid, gid and supplementary group list. */
	set_unix_security_ctx(prev_ctx_p->ut.uid,
			prev_ctx_p->ut.gid,
			prev_ctx_p->ut.ngroups,
			prev_ctx_p->ut.groups);

	/* Update current_user stuff */

	current_user.ut.uid = prev_ctx_p->ut.uid;
	current_user.ut.gid = prev_ctx_p->ut.gid;
	current_user.ut.ngroups = prev_ctx_p->ut.ngroups;
	current_user.ut.groups = prev_ctx_p->ut.groups;
	current_user.nt_user_token = prev_ctx_p->token;

	END_PROFILE(pop_sec_ctx);

	DEBUG(4, ("pop_sec_ctx (%u, %u) - sec_ctx_stack_ndx = %d\n", 
		(unsigned int)geteuid(), (unsigned int)getegid(), sec_ctx_stack_ndx));

	return True;
}

/* Initialise the security context system */

void init_sec_ctx(void)
{
	int i;
	struct sec_ctx *ctx_p;

	/* 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].ut.uid = (uid_t)-1;
		sec_ctx_stack[i].ut.gid = (gid_t)-1;
	}

	/* Initialise first level of stack.  It is the current context */
	ctx_p = &sec_ctx_stack[0];

	ctx_p->ut.uid = geteuid();
	ctx_p->ut.gid = getegid();

	get_current_groups(ctx_p->ut.gid, &ctx_p->ut.ngroups, &ctx_p->ut.groups);

	ctx_p->token = NULL; /* Maps to guest user. */

	/* Initialise current_user global */

	current_user.ut.uid = ctx_p->ut.uid;
	current_user.ut.gid = ctx_p->ut.gid;
	current_user.ut.ngroups = ctx_p->ut.ngroups;
	current_user.ut.groups = ctx_p->ut.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;
	current_user.nt_user_token = NULL;
}

/*************************************************************
 Called when we're inside a become_root() temporary escalation
 of privileges and the nt_user_token is NULL. Return the last
 active token on the context stack. We know there is at least
 one valid non-NULL token on the stack so panic if we underflow.
*************************************************************/

const struct security_token *sec_ctx_active_token(void)
{
	int stack_index = sec_ctx_stack_ndx;
	struct sec_ctx *ctx_p = &sec_ctx_stack[stack_index];

	while (ctx_p->token == NULL) {
		stack_index--;
		if (stack_index < 0) {
			DEBUG(0, ("Security context active token "
				  "stack underflow!\n"));
			smb_panic("Security context active token "
				  "stack underflow!");
		}
		ctx_p = &sec_ctx_stack[stack_index];
	}
	return ctx_p->token;
}