1 /* $NetBSD: uidswap.c,v 1.2 2009/06/07 22:38:48 christos Exp $ */ 2 /* $OpenBSD: uidswap.c,v 1.35 2006/08/03 03:34:42 deraadt Exp $ */ 3 /* 4 * Author: Tatu Ylonen <ylo@cs.hut.fi> 5 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland 6 * All rights reserved 7 * Code for uid-swapping. 8 * 9 * As far as I am concerned, the code I have written for this software 10 * can be used freely for any purpose. Any derived versions of this 11 * software must be clearly marked as such, and if the derived work is 12 * incompatible with the protocol description in the RFC file, it must be 13 * called by a name other than "ssh" or "Secure Shell". 14 */ 15 16 #include "includes.h" 17 __RCSID("$NetBSD: uidswap.c,v 1.2 2009/06/07 22:38:48 christos Exp $"); 18 #include <sys/param.h> 19 #include <errno.h> 20 #include <pwd.h> 21 #include <string.h> 22 #include <unistd.h> 23 #include <stdarg.h> 24 25 #include "log.h" 26 #include "uidswap.h" 27 28 /* 29 * Note: all these functions must work in all of the following cases: 30 * 1. euid=0, ruid=0 31 * 2. euid=0, ruid!=0 32 * 3. euid!=0, ruid!=0 33 * Additionally, they must work regardless of whether the system has 34 * POSIX saved uids or not. 35 */ 36 37 /* Lets assume that posix saved ids also work with seteuid, even though that 38 is not part of the posix specification. */ 39 40 /* Saved effective uid. */ 41 static int privileged = 0; 42 static int temporarily_use_uid_effective = 0; 43 static uid_t saved_euid = 0; 44 static gid_t saved_egid; 45 static gid_t saved_egroups[NGROUPS_MAX], user_groups[NGROUPS_MAX]; 46 static int saved_egroupslen = -1, user_groupslen = -1; 47 48 /* 49 * Temporarily changes to the given uid. If the effective user 50 * id is not root, this does nothing. This call cannot be nested. 51 */ 52 void 53 temporarily_use_uid(struct passwd *pw) 54 { 55 /* Save the current euid, and egroups. */ 56 saved_euid = geteuid(); 57 saved_egid = getegid(); 58 debug("temporarily_use_uid: %u/%u (e=%u/%u)", 59 (u_int)pw->pw_uid, (u_int)pw->pw_gid, 60 (u_int)saved_euid, (u_int)saved_egid); 61 if (saved_euid != 0) { 62 privileged = 0; 63 return; 64 } 65 privileged = 1; 66 temporarily_use_uid_effective = 1; 67 saved_egroupslen = getgroups(NGROUPS_MAX, saved_egroups); 68 if (saved_egroupslen < 0) 69 fatal("getgroups: %.100s", strerror(errno)); 70 71 /* set and save the user's groups */ 72 if (user_groupslen == -1) { 73 if (initgroups(pw->pw_name, pw->pw_gid) < 0) 74 fatal("initgroups: %s: %.100s", pw->pw_name, 75 strerror(errno)); 76 user_groupslen = getgroups(NGROUPS_MAX, user_groups); 77 if (user_groupslen < 0) 78 fatal("getgroups: %.100s", strerror(errno)); 79 } 80 /* Set the effective uid to the given (unprivileged) uid. */ 81 if (setgroups(user_groupslen, user_groups) < 0) 82 fatal("setgroups: %.100s", strerror(errno)); 83 if (setegid(pw->pw_gid) < 0) 84 fatal("setegid %u: %.100s", (u_int)pw->pw_gid, 85 strerror(errno)); 86 if (seteuid(pw->pw_uid) == -1) 87 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, 88 strerror(errno)); 89 } 90 91 /* 92 * Restores to the original (privileged) uid. 93 */ 94 void 95 restore_uid(void) 96 { 97 /* it's a no-op unless privileged */ 98 if (!privileged) { 99 debug("restore_uid: (unprivileged)"); 100 return; 101 } 102 if (!temporarily_use_uid_effective) 103 fatal("restore_uid: temporarily_use_uid not effective"); 104 debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid); 105 /* Set the effective uid back to the saved privileged uid. */ 106 if (seteuid(saved_euid) < 0) 107 fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno)); 108 if (setgroups(saved_egroupslen, saved_egroups) < 0) 109 fatal("setgroups: %.100s", strerror(errno)); 110 if (setegid(saved_egid) < 0) 111 fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno)); 112 temporarily_use_uid_effective = 0; 113 } 114 115 /* 116 * Permanently sets all uids to the given uid. This cannot be 117 * called while temporarily_use_uid is effective. 118 */ 119 void 120 permanently_set_uid(struct passwd *pw) 121 { 122 if (pw == NULL) 123 fatal("permanently_set_uid: no user given"); 124 if (temporarily_use_uid_effective) 125 fatal("permanently_set_uid: temporarily_use_uid effective"); 126 debug("permanently_set_uid: %u/%u", (u_int)pw->pw_uid, 127 (u_int)pw->pw_gid); 128 129 if (setgid(pw->pw_gid) < 0) 130 fatal("setgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); 131 if (setegid(pw->pw_gid) < 0) 132 fatal("setegid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); 133 134 if (setuid(pw->pw_uid) < 0) 135 fatal("setuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); 136 if (seteuid(pw->pw_uid) < 0) 137 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); 138 139 /* Verify GID drop was successful */ 140 if (getgid() != pw->pw_gid || getegid() != pw->pw_gid) { 141 fatal("%s: egid incorrect gid:%u egid:%u (should be %u)", 142 __func__, (u_int)getgid(), (u_int)getegid(), 143 (u_int)pw->pw_gid); 144 } 145 146 /* Verify UID drop was successful */ 147 if (getuid() != pw->pw_uid || geteuid() != pw->pw_uid) { 148 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)", 149 __func__, (u_int)getuid(), (u_int)geteuid(), 150 (u_int)pw->pw_uid); 151 } 152 } 153 154 void 155 permanently_drop_suid(uid_t uid) 156 { 157 debug("permanently_drop_suid: %u", (u_int)uid); 158 if (seteuid(uid) < 0) 159 fatal("seteuid %u: %.100s", (u_int)uid, strerror(errno)); 160 if (setuid(uid) < 0) 161 fatal("setuid %u: %.100s", (u_int)uid, strerror(errno)); 162 163 /* Verify UID drop was successful */ 164 if (getuid() != uid || geteuid() != uid) { 165 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)", 166 __func__, (u_int)getuid(), (u_int)geteuid(), (u_int)uid); 167 } 168 } 169