/* $NetBSD: uidswap.c,v 1.9.2.1 2023/12/25 12:31:10 martin Exp $ */ /* $OpenBSD: uidswap.c,v 1.42 2019/06/28 13:35:04 deraadt Exp $ */ /* * 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("$NetBSD: uidswap.c,v 1.9.2.1 2023/12/25 12:31:10 martin Exp $"); #include #include #include #include #include #include #include #include #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, user_groups_uid; 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(); 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; } privileged = 1; temporarily_use_uid_effective = 1; saved_egroupslen = getgroups(NGROUPS_MAX, saved_egroups); if (saved_egroupslen == -1) fatal("getgroups: %.100s", strerror(errno)); /* set and save the user's groups */ if (user_groupslen == -1 || user_groups_uid != pw->pw_uid) { if (initgroups(pw->pw_name, pw->pw_gid) == -1) fatal("initgroups: %s: %.100s", pw->pw_name, strerror(errno)); user_groupslen = getgroups(NGROUPS_MAX, user_groups); if (user_groupslen == -1) fatal("getgroups: %.100s", strerror(errno)); user_groups_uid = pw->pw_uid; } /* Set the effective uid to the given (unprivileged) uid. */ if (setgroups(user_groupslen, user_groups) == -1) fatal("setgroups: %.100s", strerror(errno)); if (setegid(pw->pw_gid) == -1) 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"); 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) == -1) fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno)); if (setgroups(saved_egroupslen, saved_egroups) == -1) fatal("setgroups: %.100s", strerror(errno)); if (setegid(saved_egid) == -1) 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 (pw == NULL) fatal("permanently_set_uid: no user given"); 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 (setgid(pw->pw_gid) < 0) fatal("setgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); if (setegid(pw->pw_gid) < 0) fatal("setegid %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)); if (seteuid(pw->pw_uid) < 0) fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); /* 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); } /* 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); } }