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 1.22 2002/05/28 21:24:00 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)", 56 (u_int)pw->pw_uid, (u_int)pw->pw_gid, (u_int)saved_euid); 57 if (saved_euid != 0) { 58 privileged = 0; 59 return; 60 } 61 #else 62 if (geteuid() != 0) { 63 privileged = 0; 64 return; 65 } 66 #endif /* SAVED_IDS_WORK_WITH_SETEUID */ 67 68 privileged = 1; 69 temporarily_use_uid_effective = 1; 70 saved_egroupslen = getgroups(NGROUPS_MAX, saved_egroups); 71 if (saved_egroupslen < 0) 72 fatal("getgroups: %.100s", strerror(errno)); 73 74 /* set and save the user's groups */ 75 if (user_groupslen == -1) { 76 if (initgroups(pw->pw_name, pw->pw_gid) < 0) 77 fatal("initgroups: %s: %.100s", pw->pw_name, 78 strerror(errno)); 79 user_groupslen = getgroups(NGROUPS_MAX, user_groups); 80 if (user_groupslen < 0) 81 fatal("getgroups: %.100s", strerror(errno)); 82 } 83 /* Set the effective uid to the given (unprivileged) uid. */ 84 if (setgroups(user_groupslen, user_groups) < 0) 85 fatal("setgroups: %.100s", strerror(errno)); 86 #ifndef SAVED_IDS_WORK_WITH_SETEUID 87 /* Propagate the privileged gid to all of our gids. */ 88 if (setgid(getegid()) < 0) 89 debug("setgid %u: %.100s", (u_int) getegid(), strerror(errno)); 90 /* Propagate the privileged uid to all of our uids. */ 91 if (setuid(geteuid()) < 0) 92 debug("setuid %u: %.100s", (u_int) geteuid(), strerror(errno)); 93 #endif /* SAVED_IDS_WORK_WITH_SETEUID */ 94 if (setegid(pw->pw_gid) < 0) 95 fatal("setegid %u: %.100s", (u_int)pw->pw_gid, 96 strerror(errno)); 97 if (seteuid(pw->pw_uid) == -1) 98 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, 99 strerror(errno)); 100 } 101 102 /* 103 * Restores to the original (privileged) uid. 104 */ 105 void 106 restore_uid(void) 107 { 108 debug("restore_uid"); 109 /* it's a no-op unless privileged */ 110 if (!privileged) 111 return; 112 if (!temporarily_use_uid_effective) 113 fatal("restore_uid: temporarily_use_uid not effective"); 114 115 #ifdef SAVED_IDS_WORK_WITH_SETEUID 116 /* Set the effective uid back to the saved privileged uid. */ 117 if (seteuid(saved_euid) < 0) 118 fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno)); 119 if (setegid(saved_egid) < 0) 120 fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno)); 121 #else /* SAVED_IDS_WORK_WITH_SETEUID */ 122 /* 123 * We are unable to restore the real uid to its unprivileged value. 124 * Propagate the real uid (usually more privileged) to effective uid 125 * as well. 126 */ 127 setuid(getuid()); 128 setgid(getgid()); 129 #endif /* SAVED_IDS_WORK_WITH_SETEUID */ 130 131 if (setgroups(saved_egroupslen, saved_egroups) < 0) 132 fatal("setgroups: %.100s", strerror(errno)); 133 temporarily_use_uid_effective = 0; 134 } 135 136 /* 137 * Permanently sets all uids to the given uid. This cannot be 138 * called while temporarily_use_uid is effective. 139 */ 140 void 141 permanently_set_uid(struct passwd *pw) 142 { 143 if (temporarily_use_uid_effective) 144 fatal("permanently_set_uid: temporarily_use_uid effective"); 145 if (setgid(pw->pw_gid) < 0) 146 fatal("setgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); 147 if (setuid(pw->pw_uid) < 0) 148 fatal("setuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); 149 } 150