source: branches/samba-3.2.x/source/smbd/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"

extern struct current_user current_user;

struct sec_ctx {
        UNIX_USER_TOKEN ut;
        NT_USER_TOKEN *token;
};

/* 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;

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

bool unix_token_equal(const UNIX_USER_TOKEN *t1, const UNIX_USER_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))) {
                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);

        DO_PROFILE_INC(uid_changes);
        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);
        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, int *p_ngroups, gid_t **p_groups)
{
        int i;
        gid_t grp;
        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);
        setgid(gid);

        ngroups = sys_getgroups(0,&grp);
        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( 3, ( "get_current_groups: user is in %u groups: ", ngroups));
        for (i = 0; i < ngroups; i++ ) {
                DEBUG( 3, ( "%s%d", (i ? ", " : ""), (int)groups[i] ) );
        }
        DEBUG( 3, ( "\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;

        /* 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(3, ("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;
        }

        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 %ld: %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.
****************************************************************************/

void set_sec_ctx(uid_t uid, gid_t gid, int ngroups, gid_t *groups, NT_USER_TOKEN *token)
{
        struct sec_ctx *ctx_p = &sec_ctx_stack[sec_ctx_stack_ndx];
        
        /* Set the security context */

        DEBUG(3, ("setting sec ctx (%u, %u) - sec_ctx_stack_ndx = %d\n", 
                (unsigned int)uid, (unsigned int)gid, sec_ctx_stack_ndx));

        debug_nt_user_token(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 *)memdup(groups,
                                                   sizeof(gid_t) * ngroups);
                if (!ctx_p->ut.groups) {
                        smb_panic("memdup failed");
                }
        } 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;
}

/****************************************************************************
 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, NULL);
}

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

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

        /* 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;

        DEBUG(3, ("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;
}