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/* $OpenBSD: uidswap.c,v 1.42 2019/06/28 13:35:04 deraadt Exp $ */
/*
* 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 <errno.h>
#include <pwd.h>
#include <string.h>
#include <unistd.h>
#include <limits.h>
#include <stdarg.h>
#include <stdlib.h>
#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 (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 (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) == -1)
fatal("setresgid %u: %s", (u_int)pw->pw_gid, strerror(errno));
if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) == -1)
fatal("setresuid %u: %s", (u_int)pw->pw_uid, strerror(errno));
}
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