/* * Author: Tatu Ylonen <ylo@cs.hut.fi> * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, 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 1.18 2001/08/08 21:34:19 markus Exp $"); #include "log.h" #include "uidswap.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. */ /* Lets assume that posix saved ids also work with seteuid, even though that is not part of the posix specification. */ /* Saved effective uid. */ static int privileged = 0; static int temporarily_use_uid_effective = 0; static uid_t saved_euid = 0; static gid_t saved_egid; static gid_t saved_egroups[NGROUPS_MAX], user_groups[NGROUPS_MAX]; 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. */ saved_euid = geteuid(); debug("temporarily_use_uid: %d/%d (e=%d)", pw->pw_uid, pw->pw_gid, saved_euid); if (saved_euid != 0) { privileged = 0; return; } privileged = 1; temporarily_use_uid_effective = 1; saved_egid = getegid(); saved_egroupslen = getgroups(NGROUPS_MAX, saved_egroups); if (saved_egroupslen < 0) fatal("getgroups: %.100s", strerror(errno)); /* 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(NGROUPS_MAX, user_groups); if (user_groupslen < 0) fatal("getgroups: %.100s", strerror(errno)); } /* Set the effective uid to the given (unprivileged) uid. */ if (setgroups(user_groupslen, user_groups) < 0) fatal("setgroups: %.100s", strerror(errno)); pw->pw_gid = pw->pw_gid; 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) { debug("restore_uid"); /* it's a no-op unless privileged */ if (!privileged) return; if (!temporarily_use_uid_effective) fatal("restore_uid: temporarily_use_uid not effective"); /* 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 (setgroups(saved_egroupslen, saved_egroups) < 0) fatal("setgroups: %.100s", strerror(errno)); if (setegid(saved_egid) < 0) fatal("setegid %u: %.100s", (u_int) saved_egid, 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) { if (temporarily_use_uid_effective) fatal("restore_uid: temporarily_use_uid effective"); if (setgid(pw->pw_gid) < 0) fatal("setgid %u: %.100s", (u_int) pw->pw_gid, strerror(errno)); if (setuid(pw->pw_uid) < 0) fatal("setuid %u: %.100s", (u_int) pw->pw_uid, strerror(errno)); }