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 /* Lets assume that posix saved ids also work with seteuid, even though that 30 is not part of the posix specification. */ 31 32 /* Saved effective uid. */ 33 static int privileged = 0; 34 static int temporarily_use_uid_effective = 0; 35 static uid_t saved_euid = 0; 36 static gid_t saved_egid; 37 static gid_t saved_egroups[NGROUPS_MAX], user_groups[NGROUPS_MAX]; 38 static int saved_egroupslen = -1, user_groupslen = -1; 39 40 /* 41 * Temporarily changes to the given uid. If the effective user 42 * id is not root, this does nothing. This call cannot be nested. 43 */ 44 void 45 temporarily_use_uid(struct passwd *pw) 46 { 47 /* Save the current euid, and egroups. */ 48 saved_euid = geteuid(); 49 debug("temporarily_use_uid: %u/%u (e=%u)", 50 (u_int)pw->pw_uid, (u_int)pw->pw_gid, (u_int)saved_euid); 51 if (saved_euid != 0) { 52 privileged = 0; 53 return; 54 } 55 privileged = 1; 56 temporarily_use_uid_effective = 1; 57 saved_egid = getegid(); 58 saved_egroupslen = getgroups(NGROUPS_MAX, saved_egroups); 59 if (saved_egroupslen < 0) 60 fatal("getgroups: %.100s", strerror(errno)); 61 62 /* set and save the user's groups */ 63 if (user_groupslen == -1) { 64 if (initgroups(pw->pw_name, pw->pw_gid) < 0) 65 fatal("initgroups: %s: %.100s", pw->pw_name, 66 strerror(errno)); 67 user_groupslen = getgroups(NGROUPS_MAX, user_groups); 68 if (user_groupslen < 0) 69 fatal("getgroups: %.100s", strerror(errno)); 70 } 71 /* Set the effective uid to the given (unprivileged) uid. */ 72 if (setgroups(user_groupslen, user_groups) < 0) 73 fatal("setgroups: %.100s", strerror(errno)); 74 if (setegid(pw->pw_gid) < 0) 75 fatal("setegid %u: %.100s", (u_int)pw->pw_gid, 76 strerror(errno)); 77 if (seteuid(pw->pw_uid) == -1) 78 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, 79 strerror(errno)); 80 } 81 82 /* 83 * Restores to the original (privileged) uid. 84 */ 85 void 86 restore_uid(void) 87 { 88 debug("restore_uid"); 89 /* it's a no-op unless privileged */ 90 if (!privileged) 91 return; 92 if (!temporarily_use_uid_effective) 93 fatal("restore_uid: temporarily_use_uid not effective"); 94 /* Set the effective uid back to the saved privileged uid. */ 95 if (seteuid(saved_euid) < 0) 96 fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno)); 97 if (setgroups(saved_egroupslen, saved_egroups) < 0) 98 fatal("setgroups: %.100s", strerror(errno)); 99 if (setegid(saved_egid) < 0) 100 fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno)); 101 temporarily_use_uid_effective = 0; 102 } 103 104 /* 105 * Permanently sets all uids to the given uid. This cannot be 106 * called while temporarily_use_uid is effective. 107 */ 108 void 109 permanently_set_uid(struct passwd *pw) 110 { 111 if (temporarily_use_uid_effective) 112 fatal("permanently_set_uid: temporarily_use_uid effective"); 113 if (setgid(pw->pw_gid) < 0) 114 fatal("setgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); 115 if (setuid(pw->pw_uid) < 0) 116 fatal("setuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); 117 } 118