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/* $OpenBSD: uidswap.c,v 1.39 2015/06/24 01:49:19 dtucker Exp $ */ |
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/* |
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* Author: Tatu Ylonen <ylo@cs.hut.fi> |
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* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland |
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* All rights reserved |
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* Code for uid-swapping. |
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* |
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* As far as I am concerned, the code I have written for this software |
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* can be used freely for any purpose. Any derived versions of this |
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* software must be clearly marked as such, and if the derived work is |
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* incompatible with the protocol description in the RFC file, it must be |
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* called by a name other than "ssh" or "Secure Shell". |
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*/ |
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#include <errno.h> |
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#include <pwd.h> |
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#include <string.h> |
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#include <unistd.h> |
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#include <limits.h> |
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#include <stdarg.h> |
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#include <stdlib.h> |
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#include "log.h" |
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#include "uidswap.h" |
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/* |
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* Note: all these functions must work in all of the following cases: |
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* 1. euid=0, ruid=0 |
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* 2. euid=0, ruid!=0 |
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* 3. euid!=0, ruid!=0 |
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* Additionally, they must work regardless of whether the system has |
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* POSIX saved uids or not. |
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*/ |
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/* Lets assume that posix saved ids also work with seteuid, even though that |
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is not part of the posix specification. */ |
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/* Saved effective uid. */ |
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static int privileged = 0; |
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static int temporarily_use_uid_effective = 0; |
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static uid_t saved_euid = 0; |
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static gid_t saved_egid; |
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static gid_t saved_egroups[NGROUPS_MAX], user_groups[NGROUPS_MAX]; |
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static int saved_egroupslen = -1, user_groupslen = -1; |
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/* |
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* Temporarily changes to the given uid. If the effective user |
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* id is not root, this does nothing. This call cannot be nested. |
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*/ |
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void |
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temporarily_use_uid(struct passwd *pw) |
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{ |
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/* Save the current euid, and egroups. */ |
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saved_euid = geteuid(); |
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saved_egid = getegid(); |
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debug("temporarily_use_uid: %u/%u (e=%u/%u)", |
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(u_int)pw->pw_uid, (u_int)pw->pw_gid, |
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(u_int)saved_euid, (u_int)saved_egid); |
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if (saved_euid != 0) { |
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privileged = 0; |
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return; |
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} |
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privileged = 1; |
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temporarily_use_uid_effective = 1; |
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saved_egroupslen = getgroups(NGROUPS_MAX, saved_egroups); |
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if (saved_egroupslen < 0) |
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fatal("getgroups: %.100s", strerror(errno)); |
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/* set and save the user's groups */ |
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if (user_groupslen == -1) { |
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if (initgroups(pw->pw_name, pw->pw_gid) < 0) |
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fatal("initgroups: %s: %.100s", pw->pw_name, |
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strerror(errno)); |
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user_groupslen = getgroups(NGROUPS_MAX, user_groups); |
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if (user_groupslen < 0) |
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fatal("getgroups: %.100s", strerror(errno)); |
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} |
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/* Set the effective uid to the given (unprivileged) uid. */ |
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if (setgroups(user_groupslen, user_groups) < 0) |
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fatal("setgroups: %.100s", strerror(errno)); |
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if (setegid(pw->pw_gid) < 0) |
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fatal("setegid %u: %.100s", (u_int)pw->pw_gid, |
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strerror(errno)); |
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if (seteuid(pw->pw_uid) == -1) |
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fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, |
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strerror(errno)); |
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} |
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/* |
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* Restores to the original (privileged) uid. |
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*/ |
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void |
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restore_uid(void) |
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{ |
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/* it's a no-op unless privileged */ |
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if (!privileged) { |
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debug("restore_uid: (unprivileged)"); |
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return; |
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} |
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if (!temporarily_use_uid_effective) |
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fatal("restore_uid: temporarily_use_uid not effective"); |
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debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid); |
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/* Set the effective uid back to the saved privileged uid. */ |
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if (seteuid(saved_euid) < 0) |
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fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno)); |
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if (setgroups(saved_egroupslen, saved_egroups) < 0) |
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fatal("setgroups: %.100s", strerror(errno)); |
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if (setegid(saved_egid) < 0) |
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fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno)); |
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temporarily_use_uid_effective = 0; |
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} |
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/* |
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* Permanently sets all uids to the given uid. This cannot be |
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* called while temporarily_use_uid is effective. |
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*/ |
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void |
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permanently_set_uid(struct passwd *pw) |
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{ |
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if (temporarily_use_uid_effective) |
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fatal("permanently_set_uid: temporarily_use_uid effective"); |
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debug("permanently_set_uid: %u/%u", (u_int)pw->pw_uid, |
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(u_int)pw->pw_gid); |
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if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) != 0) |
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fatal("setresgid %u: %s", (u_int)pw->pw_gid, strerror(errno)); |
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if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) != 0) |
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fatal("setresuid %u: %s", (u_int)pw->pw_uid, strerror(errno)); |
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} |
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void |
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permanently_drop_suid(uid_t uid) |
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{ |
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debug("permanently_drop_suid: %u", (u_int)uid); |
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if (setresuid(uid, uid, uid) != 0) |
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fatal("setresuid %u: %s", (u_int)uid, strerror(errno)); |
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} |