/* * Author: Tatu Ylonen * Copyright (c) 1995 Tatu Ylonen , Espoo, Finland * All rights reserved * Code for uid-swapping. * * As far as I am concerned, the code I have written for this software * can be used freely for any purpose. Any derived versions of this * software must be clearly marked as such, and if the derived work is * incompatible with the protocol description in the RFC file, it must be * called by a name other than "ssh" or "Secure Shell". */ #include "includes.h" RCSID("$OpenBSD: uidswap.c,v 1.24 2003/05/29 16:58:45 deraadt Exp $"); #include "log.h" #include "uidswap.h" #include "xmalloc.h" /* * Note: all these functions must work in all of the following cases: * 1. euid=0, ruid=0 * 2. euid=0, ruid!=0 * 3. euid!=0, ruid!=0 * Additionally, they must work regardless of whether the system has * POSIX saved uids or not. */ #if defined(_POSIX_SAVED_IDS) && !defined(BROKEN_SAVED_UIDS) /* Lets assume that posix saved ids also work with seteuid, even though that is not part of the posix specification. */ #define SAVED_IDS_WORK_WITH_SETEUID /* Saved effective uid. */ static uid_t saved_euid = 0; static gid_t saved_egid = 0; #endif /* Saved effective uid. */ static int privileged = 0; static int temporarily_use_uid_effective = 0; static gid_t *saved_egroups = NULL, *user_groups = NULL; static int saved_egroupslen = -1, user_groupslen = -1; /* * Temporarily changes to the given uid. If the effective user * id is not root, this does nothing. This call cannot be nested. */ void temporarily_use_uid(struct passwd *pw) { /* Save the current euid, and egroups. */ #ifdef SAVED_IDS_WORK_WITH_SETEUID saved_euid = geteuid(); saved_egid = getegid(); debug("temporarily_use_uid: %u/%u (e=%u/%u)", (u_int)pw->pw_uid, (u_int)pw->pw_gid, (u_int)saved_euid, (u_int)saved_egid); if (saved_euid != 0) { privileged = 0; return; } #else if (geteuid() != 0) { privileged = 0; return; } #endif /* SAVED_IDS_WORK_WITH_SETEUID */ privileged = 1; temporarily_use_uid_effective = 1; saved_egroupslen = getgroups(0, NULL); if (saved_egroupslen < 0) fatal("getgroups: %.100s", strerror(errno)); if (saved_egroupslen > 0) { saved_egroups = xrealloc(saved_egroups, saved_egroupslen * sizeof(gid_t)); if (getgroups(saved_egroupslen, saved_egroups) < 0) fatal("getgroups: %.100s", strerror(errno)); } else { /* saved_egroupslen == 0 */ if (saved_egroups) xfree(saved_egroups); } /* set and save the user's groups */ if (user_groupslen == -1) { if (initgroups(pw->pw_name, pw->pw_gid) < 0) fatal("initgroups: %s: %.100s", pw->pw_name, strerror(errno)); user_groupslen = getgroups(0, NULL); if (user_groupslen < 0) fatal("getgroups: %.100s", strerror(errno)); if (user_groupslen > 0) { user_groups = xrealloc(user_groups, user_groupslen * sizeof(gid_t)); if (getgroups(user_groupslen, user_groups) < 0) fatal("getgroups: %.100s", strerror(errno)); } else { /* user_groupslen == 0 */ if (user_groups) xfree(user_groups); } } /* Set the effective uid to the given (unprivileged) uid. */ if (setgroups(user_groupslen, user_groups) < 0) fatal("setgroups: %.100s", strerror(errno)); #ifndef SAVED_IDS_WORK_WITH_SETEUID /* Propagate the privileged gid to all of our gids. */ if (setgid(getegid()) < 0) debug("setgid %u: %.100s", (u_int) getegid(), strerror(errno)); /* Propagate the privileged uid to all of our uids. */ if (setuid(geteuid()) < 0) debug("setuid %u: %.100s", (u_int) geteuid(), strerror(errno)); #endif /* SAVED_IDS_WORK_WITH_SETEUID */ if (setegid(pw->pw_gid) < 0) fatal("setegid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); if (seteuid(pw->pw_uid) == -1) fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); } /* * Restores to the original (privileged) uid. */ void restore_uid(void) { /* it's a no-op unless privileged */ if (!privileged) { debug("restore_uid: (unprivileged)"); return; } if (!temporarily_use_uid_effective) fatal("restore_uid: temporarily_use_uid not effective"); #ifdef SAVED_IDS_WORK_WITH_SETEUID debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid); /* Set the effective uid back to the saved privileged uid. */ if (seteuid(saved_euid) < 0) fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno)); if (setegid(saved_egid) < 0) fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno)); #else /* SAVED_IDS_WORK_WITH_SETEUID */ /* * We are unable to restore the real uid to its unprivileged value. * Propagate the real uid (usually more privileged) to effective uid * as well. */ setuid(getuid()); setgid(getgid()); #endif /* SAVED_IDS_WORK_WITH_SETEUID */ if (setgroups(saved_egroupslen, saved_egroups) < 0) fatal("setgroups: %.100s", strerror(errno)); temporarily_use_uid_effective = 0; } /* * Permanently sets all uids to the given uid. This cannot be * called while temporarily_use_uid is effective. */ void permanently_set_uid(struct passwd *pw) { uid_t old_uid = getuid(); gid_t old_gid = getgid(); if (temporarily_use_uid_effective) fatal("permanently_set_uid: temporarily_use_uid effective"); debug("permanently_set_uid: %u/%u", (u_int)pw->pw_uid, (u_int)pw->pw_gid); #if defined(HAVE_SETRESGID) && !defined(BROKEN_SETRESGID) if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) < 0) fatal("setresgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); #elif defined(HAVE_SETREGID) && !defined(BROKEN_SETREGID) if (setregid(pw->pw_gid, pw->pw_gid) < 0) fatal("setregid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); #else if (setegid(pw->pw_gid) < 0) fatal("setegid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); if (setgid(pw->pw_gid) < 0) fatal("setgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); #endif #if defined(HAVE_SETRESUID) && !defined(BROKEN_SETRESUID) if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) < 0) fatal("setresuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); #elif defined(HAVE_SETREUID) && !defined(BROKEN_SETREUID) if (setreuid(pw->pw_uid, pw->pw_uid) < 0) fatal("setreuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); #else # ifndef SETEUID_BREAKS_SETUID if (seteuid(pw->pw_uid) < 0) fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); # endif if (setuid(pw->pw_uid) < 0) fatal("setuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); #endif /* Try restoration of GID if changed (test clearing of saved gid) */ if (old_gid != pw->pw_gid && (setgid(old_gid) != -1 || setegid(old_gid) != -1)) fatal("%s: was able to restore old [e]gid", __func__); /* Verify GID drop was successful */ if (getgid() != pw->pw_gid || getegid() != pw->pw_gid) { fatal("%s: egid incorrect gid:%u egid:%u (should be %u)", __func__, (u_int)getgid(), (u_int)getegid(), (u_int)pw->pw_gid); } #ifndef HAVE_CYGWIN /* Try restoration of UID if changed (test clearing of saved uid) */ if (old_uid != pw->pw_uid && (setuid(old_uid) != -1 || seteuid(old_uid) != -1)) fatal("%s: was able to restore old [e]uid", __func__); #endif /* Verify UID drop was successful */ if (getuid() != pw->pw_uid || geteuid() != pw->pw_uid) { fatal("%s: euid incorrect uid:%u euid:%u (should be %u)", __func__, (u_int)getuid(), (u_int)geteuid(), (u_int)pw->pw_uid); } }