uidswap.c revision 60573 
1/*
2 * Author: Tatu Ylonen <ylo@cs.hut.fi>
3 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
4 *                    All rights reserved
5 * Created: Sat Sep  9 01:56:14 1995 ylo
6 * Code for uid-swapping.
7 */
8
9#include "includes.h"
10RCSID("$Id: uidswap.c,v 1.6 2000/04/14 10:30:34 markus Exp $");
11
12#include "ssh.h"
13#include "uidswap.h"
14
15/*
16 * Note: all these functions must work in all of the following cases:
17 *    1. euid=0, ruid=0
18 *    2. euid=0, ruid!=0
19 *    3. euid!=0, ruid!=0
20 * Additionally, they must work regardless of whether the system has
21 * POSIX saved uids or not.
22 */
23
24#ifdef _POSIX_SAVED_IDS
25/* Lets assume that posix saved ids also work with seteuid, even though that
26   is not part of the posix specification. */
27#define SAVED_IDS_WORK_WITH_SETEUID
28#endif /* _POSIX_SAVED_IDS */
29
30/* Saved effective uid. */
31static uid_t saved_euid = 0;
32
33/*
34 * Temporarily changes to the given uid.  If the effective user
35 * id is not root, this does nothing.  This call cannot be nested.
36 */
37void
38temporarily_use_uid(uid_t uid)
39{
40#ifdef SAVED_IDS_WORK_WITH_SETEUID
41	/* Save the current euid. */
42	saved_euid = geteuid();
43
44	/* Set the effective uid to the given (unprivileged) uid. */
45	if (seteuid(uid) == -1)
46		debug("seteuid %d: %.100s", (int) uid, strerror(errno));
47#else /* SAVED_IDS_WORK_WITH_SETUID */
48	/* Propagate the privileged uid to all of our uids. */
49	if (setuid(geteuid()) < 0)
50		debug("setuid %d: %.100s", (int) geteuid(), strerror(errno));
51
52	/* Set the effective uid to the given (unprivileged) uid. */
53	if (seteuid(uid) == -1)
54		debug("seteuid %d: %.100s", (int) uid, strerror(errno));
55#endif /* SAVED_IDS_WORK_WITH_SETEUID */
56}
57
58/*
59 * Restores to the original uid.
60 */
61void
62restore_uid()
63{
64#ifdef SAVED_IDS_WORK_WITH_SETEUID
65	/* Set the effective uid back to the saved uid. */
66	if (seteuid(saved_euid) < 0)
67		debug("seteuid %d: %.100s", (int) saved_euid, strerror(errno));
68#else /* SAVED_IDS_WORK_WITH_SETEUID */
69	/*
70	 * We are unable to restore the real uid to its unprivileged value.
71	 * Propagate the real uid (usually more privileged) to effective uid
72	 * as well.
73	 */
74	setuid(getuid());
75#endif /* SAVED_IDS_WORK_WITH_SETEUID */
76}
77
78/*
79 * Permanently sets all uids to the given uid.  This cannot be
80 * called while temporarily_use_uid is effective.
81 */
82void
83permanently_set_uid(uid_t uid)
84{
85	if (setuid(uid) < 0)
86		debug("setuid %d: %.100s", (int) uid, strerror(errno));
87}
88