Annotation of src/usr.bin/ssh/uidswap.c, Revision 1.40
1.40 ! djm 1: /* $OpenBSD: uidswap.c,v 1.39 2015/06/24 01:49:19 dtucker Exp $ */
1.1 deraadt 2: /*
1.4 deraadt 3: * Author: Tatu Ylonen <ylo@cs.hut.fi>
4: * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
5: * All rights reserved
6: * Code for uid-swapping.
1.9 deraadt 7: *
8: * As far as I am concerned, the code I have written for this software
9: * can be used freely for any purpose. Any derived versions of this
10: * software must be clearly marked as such, and if the derived work is
11: * incompatible with the protocol description in the RFC file, it must be
12: * called by a name other than "ssh" or "Secure Shell".
1.4 deraadt 13: */
1.1 deraadt 14:
1.31 stevesk 15: #include <errno.h>
1.30 stevesk 16: #include <pwd.h>
1.33 stevesk 17: #include <string.h>
1.32 stevesk 18: #include <unistd.h>
1.37 deraadt 19: #include <limits.h>
1.35 deraadt 20: #include <stdarg.h>
1.36 dtucker 21: #include <stdlib.h>
1.1 deraadt 22:
1.13 markus 23: #include "log.h"
1.1 deraadt 24: #include "uidswap.h"
25:
1.4 deraadt 26: /*
27: * Note: all these functions must work in all of the following cases:
28: * 1. euid=0, ruid=0
29: * 2. euid=0, ruid!=0
30: * 3. euid!=0, ruid!=0
31: * Additionally, they must work regardless of whether the system has
32: * POSIX saved uids or not.
33: */
1.1 deraadt 34:
35: /* Lets assume that posix saved ids also work with seteuid, even though that
36: is not part of the posix specification. */
1.14 markus 37:
1.1 deraadt 38: /* Saved effective uid. */
1.14 markus 39: static int privileged = 0;
40: static int temporarily_use_uid_effective = 0;
1.40 ! djm 41: static uid_t saved_euid, user_groups_uid;
1.14 markus 42: static gid_t saved_egid;
43: static gid_t saved_egroups[NGROUPS_MAX], user_groups[NGROUPS_MAX];
44: static int saved_egroupslen = -1, user_groupslen = -1;
1.1 deraadt 45:
1.4 deraadt 46: /*
47: * Temporarily changes to the given uid. If the effective user
48: * id is not root, this does nothing. This call cannot be nested.
49: */
1.6 markus 50: void
1.14 markus 51: temporarily_use_uid(struct passwd *pw)
1.1 deraadt 52: {
1.14 markus 53: /* Save the current euid, and egroups. */
1.3 markus 54: saved_euid = geteuid();
1.23 stevesk 55: saved_egid = getegid();
56: debug("temporarily_use_uid: %u/%u (e=%u/%u)",
57: (u_int)pw->pw_uid, (u_int)pw->pw_gid,
58: (u_int)saved_euid, (u_int)saved_egid);
1.14 markus 59: if (saved_euid != 0) {
60: privileged = 0;
61: return;
62: }
63: privileged = 1;
64: temporarily_use_uid_effective = 1;
1.19 deraadt 65: saved_egroupslen = getgroups(NGROUPS_MAX, saved_egroups);
1.14 markus 66: if (saved_egroupslen < 0)
67: fatal("getgroups: %.100s", strerror(errno));
68:
69: /* set and save the user's groups */
1.40 ! djm 70: if (user_groupslen == -1 || user_groups_uid != pw->pw_uid) {
1.14 markus 71: if (initgroups(pw->pw_name, pw->pw_gid) < 0)
72: fatal("initgroups: %s: %.100s", pw->pw_name,
73: strerror(errno));
1.19 deraadt 74: user_groupslen = getgroups(NGROUPS_MAX, user_groups);
1.14 markus 75: if (user_groupslen < 0)
76: fatal("getgroups: %.100s", strerror(errno));
1.40 ! djm 77: user_groups_uid = pw->pw_uid;
1.14 markus 78: }
1.3 markus 79: /* Set the effective uid to the given (unprivileged) uid. */
1.39 dtucker 80: if (setgroups(user_groupslen, user_groups) < 0)
1.14 markus 81: fatal("setgroups: %.100s", strerror(errno));
1.15 markus 82: if (setegid(pw->pw_gid) < 0)
1.21 stevesk 83: fatal("setegid %u: %.100s", (u_int)pw->pw_gid,
1.14 markus 84: strerror(errno));
85: if (seteuid(pw->pw_uid) == -1)
1.21 stevesk 86: fatal("seteuid %u: %.100s", (u_int)pw->pw_uid,
1.14 markus 87: strerror(errno));
1.1 deraadt 88: }
89:
1.4 deraadt 90: /*
1.16 markus 91: * Restores to the original (privileged) uid.
1.4 deraadt 92: */
1.6 markus 93: void
1.11 markus 94: restore_uid(void)
1.1 deraadt 95: {
1.14 markus 96: /* it's a no-op unless privileged */
1.23 stevesk 97: if (!privileged) {
98: debug("restore_uid: (unprivileged)");
1.14 markus 99: return;
1.23 stevesk 100: }
1.14 markus 101: if (!temporarily_use_uid_effective)
102: fatal("restore_uid: temporarily_use_uid not effective");
1.23 stevesk 103: debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid);
1.16 markus 104: /* Set the effective uid back to the saved privileged uid. */
1.3 markus 105: if (seteuid(saved_euid) < 0)
1.21 stevesk 106: fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno));
1.39 dtucker 107: if (setgroups(saved_egroupslen, saved_egroups) < 0)
1.14 markus 108: fatal("setgroups: %.100s", strerror(errno));
1.15 markus 109: if (setegid(saved_egid) < 0)
1.21 stevesk 110: fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno));
1.14 markus 111: temporarily_use_uid_effective = 0;
1.1 deraadt 112: }
113:
1.4 deraadt 114: /*
115: * Permanently sets all uids to the given uid. This cannot be
116: * called while temporarily_use_uid is effective.
117: */
1.6 markus 118: void
1.14 markus 119: permanently_set_uid(struct passwd *pw)
1.1 deraadt 120: {
1.14 markus 121: if (temporarily_use_uid_effective)
1.22 stevesk 122: fatal("permanently_set_uid: temporarily_use_uid effective");
1.23 stevesk 123: debug("permanently_set_uid: %u/%u", (u_int)pw->pw_uid,
124: (u_int)pw->pw_gid);
1.27 djm 125: if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) != 0)
126: fatal("setresgid %u: %s", (u_int)pw->pw_gid, strerror(errno));
127: if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) != 0)
128: fatal("setresuid %u: %s", (u_int)pw->pw_uid, strerror(errno));
1.29 markus 129: }
130:
131: void
132: permanently_drop_suid(uid_t uid)
133: {
134: debug("permanently_drop_suid: %u", (u_int)uid);
135: if (setresuid(uid, uid, uid) != 0)
136: fatal("setresuid %u: %s", (u_int)uid, strerror(errno));
1.1 deraadt 137: }
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