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 * Code for uid-swapping. 6 * 7 * As far as I am concerned, the code I have written for this software 8 * can be used freely for any purpose. Any derived versions of this 9 * software must be clearly marked as such, and if the derived work is 10 * incompatible with the protocol description in the RFC file, it must be 11 * called by a name other than "ssh" or "Secure Shell". 12 */ 13 14 #include "includes.h" 15 RCSID("$OpenBSD: uidswap.c,v 1.23 2002/07/15 17:15:31 stevesk Exp $"); 16 17 #include "log.h" 18 #include "uidswap.h" 19 20 /* 21 * Note: all these functions must work in all of the following cases: 22 * 1. euid=0, ruid=0 23 * 2. euid=0, ruid!=0 24 * 3. euid!=0, ruid!=0 25 * Additionally, they must work regardless of whether the system has 26 * POSIX saved uids or not. 27 */ 28 29 #if defined(_POSIX_SAVED_IDS) && !defined(BROKEN_SAVED_UIDS) 30 /* Lets assume that posix saved ids also work with seteuid, even though that 31 is not part of the posix specification. */ 32 #define SAVED_IDS_WORK_WITH_SETEUID 33 /* Saved effective uid. */ 34 static uid_t saved_euid = 0; 35 static gid_t saved_egid = 0; 36 #endif 37 38 /* Saved effective uid. */ 39 static int privileged = 0; 40 static int temporarily_use_uid_effective = 0; 41 static gid_t saved_egroups[NGROUPS_MAX], user_groups[NGROUPS_MAX]; 42 static int saved_egroupslen = -1, user_groupslen = -1; 43 44 /* 45 * Temporarily changes to the given uid. If the effective user 46 * id is not root, this does nothing. This call cannot be nested. 47 */ 48 void 49 temporarily_use_uid(struct passwd *pw) 50 { 51 /* Save the current euid, and egroups. */ 52 #ifdef SAVED_IDS_WORK_WITH_SETEUID 53 saved_euid = geteuid(); 54 saved_egid = getegid(); 55 debug("temporarily_use_uid: %u/%u (e=%u/%u)", 56 (u_int)pw->pw_uid, (u_int)pw->pw_gid, 57 (u_int)saved_euid, (u_int)saved_egid); 58 if (saved_euid != 0) { 59 privileged = 0; 60 return; 61 } 62 #else 63 if (geteuid() != 0) { 64 privileged = 0; 65 return; 66 } 67 #endif /* SAVED_IDS_WORK_WITH_SETEUID */ 68 69 privileged = 1; 70 temporarily_use_uid_effective = 1; 71 saved_egroupslen = getgroups(NGROUPS_MAX, saved_egroups); 72 if (saved_egroupslen < 0) 73 fatal("getgroups: %.100s", strerror(errno)); 74 75 /* set and save the user's groups */ 76 if (user_groupslen == -1) { 77 if (initgroups(pw->pw_name, pw->pw_gid) < 0) 78 fatal("initgroups: %s: %.100s", pw->pw_name, 79 strerror(errno)); 80 user_groupslen = getgroups(NGROUPS_MAX, user_groups); 81 if (user_groupslen < 0) 82 fatal("getgroups: %.100s", strerror(errno)); 83 } 84 /* Set the effective uid to the given (unprivileged) uid. */ 85 if (setgroups(user_groupslen, user_groups) < 0) 86 fatal("setgroups: %.100s", strerror(errno)); 87 #ifndef SAVED_IDS_WORK_WITH_SETEUID 88 /* Propagate the privileged gid to all of our gids. */ 89 if (setgid(getegid()) < 0) 90 debug("setgid %u: %.100s", (u_int) getegid(), strerror(errno)); 91 /* Propagate the privileged uid to all of our uids. */ 92 if (setuid(geteuid()) < 0) 93 debug("setuid %u: %.100s", (u_int) geteuid(), strerror(errno)); 94 #endif /* SAVED_IDS_WORK_WITH_SETEUID */ 95 if (setegid(pw->pw_gid) < 0) 96 fatal("setegid %u: %.100s", (u_int)pw->pw_gid, 97 strerror(errno)); 98 if (seteuid(pw->pw_uid) == -1) 99 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, 100 strerror(errno)); 101 } 102 103 /* 104 * Restores to the original (privileged) uid. 105 */ 106 void 107 restore_uid(void) 108 { 109 /* it's a no-op unless privileged */ 110 if (!privileged) { 111 debug("restore_uid: (unprivileged)"); 112 return; 113 } 114 if (!temporarily_use_uid_effective) 115 fatal("restore_uid: temporarily_use_uid not effective"); 116 117 #ifdef SAVED_IDS_WORK_WITH_SETEUID 118 debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid); 119 /* Set the effective uid back to the saved privileged uid. */ 120 if (seteuid(saved_euid) < 0) 121 fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno)); 122 if (setegid(saved_egid) < 0) 123 fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno)); 124 #else /* SAVED_IDS_WORK_WITH_SETEUID */ 125 /* 126 * We are unable to restore the real uid to its unprivileged value. 127 * Propagate the real uid (usually more privileged) to effective uid 128 * as well. 129 */ 130 setuid(getuid()); 131 setgid(getgid()); 132 #endif /* SAVED_IDS_WORK_WITH_SETEUID */ 133 134 if (setgroups(saved_egroupslen, saved_egroups) < 0) 135 fatal("setgroups: %.100s", strerror(errno)); 136 temporarily_use_uid_effective = 0; 137 } 138 139 /* 140 * Permanently sets all uids to the given uid. This cannot be 141 * called while temporarily_use_uid is effective. 142 */ 143 void 144 permanently_set_uid(struct passwd *pw) 145 { 146 if (temporarily_use_uid_effective) 147 fatal("permanently_set_uid: temporarily_use_uid effective"); 148 debug("permanently_set_uid: %u/%u", (u_int)pw->pw_uid, 149 (u_int)pw->pw_gid); 150 if (setgid(pw->pw_gid) < 0) 151 fatal("setgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); 152 if (setuid(pw->pw_uid) < 0) 153 fatal("setuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); 154 } 155