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Drop privileges by default when opening user-related files
The module is typically executed as root and would sometimes open files or follow symlinks that could be controlled from the outside. Drop privileges to the target user before opening any files. Fixes CVE-2019-12209. Thanks to Matthias Gerstner of the SUSE Security Team for reporting the issue.
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Gabriel Kihlman
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Jun 4, 2019
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,129 @@ | ||
| /* Written by Ricky Zhou <ricky@fedoraproject.org> | ||
| * Fredrik Thulin <fredrik@yubico.com> implemented pam_modutil_drop_priv | ||
| * | ||
| * Copyright (c) 2011-2014 Yubico AB | ||
| * Copyright (c) 2011 Ricky Zhou <ricky@fedoraproject.org> | ||
| * All rights reserved. | ||
| * | ||
| * Redistribution and use in source and binary forms, with or without | ||
| * modification, are permitted provided that the following conditions are | ||
| * met: | ||
| * | ||
| * * Redistributions of source code must retain the above copyright | ||
| * notice, this list of conditions and the following disclaimer. | ||
| * | ||
| * * Redistributions in binary form must reproduce the above | ||
| * copyright notice, this list of conditions and the following | ||
| * disclaimer in the documentation and/or other materials provided | ||
| * with the distribution. | ||
| * | ||
| * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS | ||
| * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT | ||
| * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR | ||
| * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT | ||
| * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, | ||
| * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT | ||
| * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, | ||
| * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY | ||
| * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT | ||
| * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE | ||
| * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. | ||
| */ | ||
|
|
||
| #ifndef HAVE_PAM_MODUTIL_DROP_PRIV | ||
|
|
||
| #include <unistd.h> | ||
| #include <pwd.h> | ||
| #include <grp.h> | ||
| #include <errno.h> | ||
| #include <string.h> | ||
| #include <stdlib.h> | ||
|
|
||
| #include "drop_privs.h" | ||
| #include "util.h" | ||
|
|
||
| #ifdef HAVE_SECURITY_PAM_APPL_H | ||
| #include <security/pam_appl.h> | ||
| #endif | ||
| #ifdef HAVE_SECURITY_PAM_MODULES_H | ||
| #include <security/pam_modules.h> | ||
| #endif | ||
|
|
||
|
|
||
| int pam_modutil_drop_priv(pam_handle_t *pamh, struct _ykpam_privs *privs, struct passwd *pw) { | ||
| privs->saved_euid = geteuid(); | ||
| privs->saved_egid = getegid(); | ||
|
|
||
| if ((privs->saved_euid == pw->pw_uid) && (privs->saved_egid == pw->pw_gid)) { | ||
| D (privs->debug_file, "Privilges already dropped, pretend it is all right"); | ||
| return 0; | ||
| } | ||
|
|
||
| privs->saved_groups_length = getgroups(0, NULL); | ||
| if (privs->saved_groups_length < 0) { | ||
| D (privs->debug_file, "getgroups: %s", strerror(errno)); | ||
| return -1; | ||
| } | ||
|
|
||
| if (privs->saved_groups_length > SAVED_GROUPS_MAX_LEN) { | ||
| D (privs->debug_file, "too many groups, limiting."); | ||
| privs->saved_groups_length = SAVED_GROUPS_MAX_LEN; | ||
| } | ||
|
|
||
| if (privs->saved_groups_length > 0) { | ||
| if (getgroups(privs->saved_groups_length, privs->saved_groups) < 0) { | ||
| D (privs->debug_file, "getgroups: %s", strerror(errno)); | ||
| goto free_out; | ||
| } | ||
| } | ||
|
|
||
| if (initgroups(pw->pw_name, pw->pw_gid) < 0) { | ||
| D (privs->debug_file, "initgroups: %s", strerror(errno)); | ||
| goto free_out; | ||
| } | ||
|
|
||
| if (setegid(pw->pw_gid) < 0) { | ||
| D (privs->debug_file, "setegid: %s", strerror(errno)); | ||
| goto free_out; | ||
| } | ||
|
|
||
| if (seteuid(pw->pw_uid) < 0) { | ||
| D (privs->debug_file, "seteuid: %s", strerror(errno)); | ||
| goto free_out; | ||
| } | ||
|
|
||
| return 0; | ||
| free_out: | ||
| return -1; | ||
| } | ||
|
|
||
| int pam_modutil_regain_priv(pam_handle_t *pamh, struct _ykpam_privs *privs) { | ||
| if ((privs->saved_euid == geteuid()) && (privs->saved_egid == getegid())) { | ||
| D (privs->debug_file, "Privilges already as requested, pretend it is all right"); | ||
| return 0; | ||
| } | ||
|
|
||
| if (seteuid(privs->saved_euid) < 0) { | ||
| D (privs->debug_file, "seteuid: %s", strerror(errno)); | ||
| return -1; | ||
| } | ||
|
|
||
| if (setegid(privs->saved_egid) < 0) { | ||
| D (privs->debug_file, "setegid: %s", strerror(errno)); | ||
| return -1; | ||
| } | ||
|
|
||
| if (setgroups(privs->saved_groups_length, privs->saved_groups) < 0) { | ||
| D (privs->debug_file, "setgroups: %s", strerror(errno)); | ||
| return -1; | ||
| } | ||
|
|
||
| return 0; | ||
| } | ||
|
|
||
| #else | ||
|
|
||
| // drop_privs.c:124: warning: ISO C forbids an empty translation unit [-Wpedantic] | ||
| typedef int make_iso_compilers_happy; | ||
|
|
||
| #endif // HAVE_PAM_MODUTIL_DROP_PRIV |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,64 @@ | ||
| /* Copyright (c) 2011-2014 Yubico AB | ||
| * All rights reserved. | ||
| * | ||
| * Redistribution and use in source and binary forms, with or without | ||
| * modification, are permitted provided that the following conditions are | ||
| * met: | ||
| * | ||
| * * Redistributions of source code must retain the above copyright | ||
| * notice, this list of conditions and the following disclaimer. | ||
| * | ||
| * * Redistributions in binary form must reproduce the above | ||
| * copyright notice, this list of conditions and the following | ||
| * disclaimer in the documentation and/or other materials provided | ||
| * with the distribution. | ||
| * | ||
| * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS | ||
| * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT | ||
| * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR | ||
| * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT | ||
| * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, | ||
| * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT | ||
| * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, | ||
| * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY | ||
| * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT | ||
| * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE | ||
| * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. | ||
| */ | ||
|
|
||
| #ifndef __PAM_U2F_DROP_PRIVS_H_INCLUDED__ | ||
| #define __PAM_U2F_DROP_PRIVS_H_INCLUDED__ | ||
|
|
||
| #ifdef HAVE_PAM_MODUTIL_DROP_PRIV | ||
| #include <security/pam_modutil.h> | ||
| #else | ||
|
|
||
| #include <pwd.h> | ||
| #include <stdio.h> | ||
|
|
||
| #ifdef HAVE_SECURITY_PAM_APPL_H | ||
| #include <security/pam_appl.h> | ||
| #endif | ||
| #ifdef HAVE_SECURITY_PAM_MODULES_H | ||
| #include <security/pam_modules.h> | ||
| #endif | ||
|
|
||
| #define SAVED_GROUPS_MAX_LEN 64 /* as pam_modutil.. */ | ||
|
|
||
| struct _ykpam_privs { | ||
| uid_t saved_euid; | ||
| gid_t saved_egid; | ||
| gid_t *saved_groups; | ||
| int saved_groups_length; | ||
| FILE *debug_file; | ||
| }; | ||
|
|
||
| #define PAM_MODUTIL_DEF_PRIVS(n) \ | ||
| gid_t n##_saved_groups[SAVED_GROUPS_MAX_LEN]; \ | ||
| struct _ykpam_privs n = {-1, -1, n##_saved_groups, SAVED_GROUPS_MAX_LEN, cfg->debug_file} | ||
|
|
||
| int pam_modutil_drop_priv(pam_handle_t *, struct _ykpam_privs *, struct passwd *); | ||
| int pam_modutil_regain_priv(pam_handle_t *, struct _ykpam_privs *); | ||
|
|
||
| #endif | ||
| #endif |
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