1/* $NetBSD: uidswap.c,v 1.10 2019/10/12 18:32:22 christos Exp $ */ 2/* $OpenBSD: uidswap.c,v 1.42 2019/06/28 13:35:04 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 1.10 2019/10/12 18:32:22 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 <limits.h> 24#include <stdarg.h> 25#include <stdlib.h> 26 27#include "log.h" 28#include "uidswap.h" 29 30/* 31 * Note: all these functions must work in all of the following cases: 32 * 1. euid=0, ruid=0 33 * 2. euid=0, ruid!=0 34 * 3. euid!=0, ruid!=0 35 * Additionally, they must work regardless of whether the system has 36 * POSIX saved uids or not. 37 */ 38 39/* Lets assume that posix saved ids also work with seteuid, even though that 40 is not part of the posix specification. */ 41 42/* Saved effective uid. */ 43static int privileged = 0; 44static int temporarily_use_uid_effective = 0; 45static uid_t saved_euid, user_groups_uid; 46static gid_t saved_egid; 47static gid_t saved_egroups[NGROUPS_MAX], user_groups[NGROUPS_MAX]; 48static int saved_egroupslen = -1, user_groupslen = -1; 49 50/* 51 * Temporarily changes to the given uid. If the effective user 52 * id is not root, this does nothing. This call cannot be nested. 53 */ 54void 55temporarily_use_uid(struct passwd *pw) 56{ 57 /* Save the current euid, and egroups. */ 58 saved_euid = geteuid(); 59 saved_egid = getegid(); 60 debug("temporarily_use_uid: %u/%u (e=%u/%u)", 61 (u_int)pw->pw_uid, (u_int)pw->pw_gid, 62 (u_int)saved_euid, (u_int)saved_egid); 63 if (saved_euid != 0) { 64 privileged = 0; 65 return; 66 } 67 privileged = 1; 68 temporarily_use_uid_effective = 1; 69 saved_egroupslen = getgroups(NGROUPS_MAX, saved_egroups); 70 if (saved_egroupslen == -1) 71 fatal("getgroups: %.100s", strerror(errno)); 72 73 /* set and save the user's groups */ 74 if (user_groupslen == -1 || user_groups_uid != pw->pw_uid) { 75 if (initgroups(pw->pw_name, pw->pw_gid) == -1) 76 fatal("initgroups: %s: %.100s", pw->pw_name, 77 strerror(errno)); 78 user_groupslen = getgroups(NGROUPS_MAX, user_groups); 79 if (user_groupslen == -1) 80 fatal("getgroups: %.100s", strerror(errno)); 81 user_groups_uid = pw->pw_uid; 82 } 83 /* Set the effective uid to the given (unprivileged) uid. */ 84 if (setgroups(user_groupslen, user_groups) == -1) 85 fatal("setgroups: %.100s", strerror(errno)); 86 if (setegid(pw->pw_gid) == -1) 87 fatal("setegid %u: %.100s", (u_int)pw->pw_gid, 88 strerror(errno)); 89 if (seteuid(pw->pw_uid) == -1) 90 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, 91 strerror(errno)); 92} 93 94/* 95 * Restores to the original (privileged) uid. 96 */ 97void 98restore_uid(void) 99{ 100 /* it's a no-op unless privileged */ 101 if (!privileged) { 102 debug("restore_uid: (unprivileged)"); 103 return; 104 } 105 if (!temporarily_use_uid_effective) 106 fatal("restore_uid: temporarily_use_uid not effective"); 107 debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid); 108 /* Set the effective uid back to the saved privileged uid. */ 109 if (seteuid(saved_euid) == -1) 110 fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno)); 111 if (setgroups(saved_egroupslen, saved_egroups) == -1) 112 fatal("setgroups: %.100s", strerror(errno)); 113 if (setegid(saved_egid) == -1) 114 fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno)); 115 temporarily_use_uid_effective = 0; 116} 117 118/* 119 * Permanently sets all uids to the given uid. This cannot be 120 * called while temporarily_use_uid is effective. 121 */ 122void 123permanently_set_uid(struct passwd *pw) 124{ 125 if (pw == NULL) 126 fatal("permanently_set_uid: no user given"); 127 if (temporarily_use_uid_effective) 128 fatal("permanently_set_uid: temporarily_use_uid effective"); 129 debug("permanently_set_uid: %u/%u", (u_int)pw->pw_uid, 130 (u_int)pw->pw_gid); 131 132 if (setgid(pw->pw_gid) < 0) 133 fatal("setgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); 134 if (setegid(pw->pw_gid) < 0) 135 fatal("setegid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); 136 137 if (setuid(pw->pw_uid) < 0) 138 fatal("setuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); 139 if (seteuid(pw->pw_uid) < 0) 140 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); 141 142 /* Verify GID drop was successful */ 143 if (getgid() != pw->pw_gid || getegid() != pw->pw_gid) { 144 fatal("%s: egid incorrect gid:%u egid:%u (should be %u)", 145 __func__, (u_int)getgid(), (u_int)getegid(), 146 (u_int)pw->pw_gid); 147 } 148 149 /* Verify UID drop was successful */ 150 if (getuid() != pw->pw_uid || geteuid() != pw->pw_uid) { 151 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)", 152 __func__, (u_int)getuid(), (u_int)geteuid(), 153 (u_int)pw->pw_uid); 154 } 155} 156