1 /* $OpenBSD: uidswap.c,v 1.39 2015/06/24 01:49:19 dtucker Exp $ */ 2 /* 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. 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". 13 */ 14 15 #include <errno.h> 16 #include <pwd.h> 17 #include <string.h> 18 #include <unistd.h> 19 #include <limits.h> 20 #include <stdarg.h> 21 #include <stdlib.h> 22 23 #include "log.h" 24 #include "uidswap.h" 25 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 */ 34 35 /* Lets assume that posix saved ids also work with seteuid, even though that 36 is not part of the posix specification. */ 37 38 /* Saved effective uid. */ 39 static int privileged = 0; 40 static int temporarily_use_uid_effective = 0; 41 static uid_t saved_euid = 0; 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; 45 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 */ 50 void 51 temporarily_use_uid(struct passwd *pw) 52 { 53 /* Save the current euid, and egroups. */ 54 saved_euid = geteuid(); 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); 59 if (saved_euid != 0) { 60 privileged = 0; 61 return; 62 } 63 privileged = 1; 64 temporarily_use_uid_effective = 1; 65 saved_egroupslen = getgroups(NGROUPS_MAX, saved_egroups); 66 if (saved_egroupslen < 0) 67 fatal("getgroups: %.100s", strerror(errno)); 68 69 /* set and save the user's groups */ 70 if (user_groupslen == -1) { 71 if (initgroups(pw->pw_name, pw->pw_gid) < 0) 72 fatal("initgroups: %s: %.100s", pw->pw_name, 73 strerror(errno)); 74 user_groupslen = getgroups(NGROUPS_MAX, user_groups); 75 if (user_groupslen < 0) 76 fatal("getgroups: %.100s", strerror(errno)); 77 } 78 /* Set the effective uid to the given (unprivileged) uid. */ 79 if (setgroups(user_groupslen, user_groups) < 0) 80 fatal("setgroups: %.100s", strerror(errno)); 81 if (setegid(pw->pw_gid) < 0) 82 fatal("setegid %u: %.100s", (u_int)pw->pw_gid, 83 strerror(errno)); 84 if (seteuid(pw->pw_uid) == -1) 85 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, 86 strerror(errno)); 87 } 88 89 /* 90 * Restores to the original (privileged) uid. 91 */ 92 void 93 restore_uid(void) 94 { 95 /* it's a no-op unless privileged */ 96 if (!privileged) { 97 debug("restore_uid: (unprivileged)"); 98 return; 99 } 100 if (!temporarily_use_uid_effective) 101 fatal("restore_uid: temporarily_use_uid not effective"); 102 debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid); 103 /* Set the effective uid back to the saved privileged uid. */ 104 if (seteuid(saved_euid) < 0) 105 fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno)); 106 if (setgroups(saved_egroupslen, saved_egroups) < 0) 107 fatal("setgroups: %.100s", strerror(errno)); 108 if (setegid(saved_egid) < 0) 109 fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno)); 110 temporarily_use_uid_effective = 0; 111 } 112 113 /* 114 * Permanently sets all uids to the given uid. This cannot be 115 * called while temporarily_use_uid is effective. 116 */ 117 void 118 permanently_set_uid(struct passwd *pw) 119 { 120 if (temporarily_use_uid_effective) 121 fatal("permanently_set_uid: temporarily_use_uid effective"); 122 debug("permanently_set_uid: %u/%u", (u_int)pw->pw_uid, 123 (u_int)pw->pw_gid); 124 if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) != 0) 125 fatal("setresgid %u: %s", (u_int)pw->pw_gid, strerror(errno)); 126 if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) != 0) 127 fatal("setresuid %u: %s", (u_int)pw->pw_uid, strerror(errno)); 128 } 129 130 void 131 permanently_drop_suid(uid_t uid) 132 { 133 debug("permanently_drop_suid: %u", (u_int)uid); 134 if (setresuid(uid, uid, uid) != 0) 135 fatal("setresuid %u: %s", (u_int)uid, strerror(errno)); 136 } 137