From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7A993C433EF for ; Wed, 1 Jun 2022 10:11:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1348665AbiFAKK7 (ORCPT ); Wed, 1 Jun 2022 06:10:59 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33872 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1352394AbiFAKKe (ORCPT ); Wed, 1 Jun 2022 06:10:34 -0400 Received: from mx0a-00069f02.pphosted.com (mx0a-00069f02.pphosted.com [205.220.165.32]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 128DF303; Wed, 1 Jun 2022 03:10:22 -0700 (PDT) Received: from pps.filterd (m0246617.ppops.net [127.0.0.1]) by mx0b-00069f02.pphosted.com (8.17.1.5/8.17.1.5) with ESMTP id 2519ZP92022518; Wed, 1 Jun 2022 10:09:59 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=from : to : cc : subject : date : message-id : in-reply-to : references : mime-version : content-transfer-encoding; s=corp-2021-07-09; bh=1cBsXF30SKlnex84x05Ujxeu15q8/iwZ2bkoaVDadmg=; b=huIeKacQy1oSQR0ETJGJqMR7WMzNyCZgl0FdPUBd4twQ3yKqYSonlSlwM4CcWfotvEwQ ny3EkfhBUjNixJJl5+i3wmZE9MRNTuYLOpV8cEkmMNB9acMQ2vbcaUhvp3Yw+LWpKROu pW4R9SS5NTQEvwQ3nHNKiZ4MEoXBw8Gz7e86SDpeGGEYbnRIOCXS65YYFfO1ci2ZJpke 2mOr9CRr5fE+D32cEukxnN5TryLGwswF54OIIWIpH7QRA4p/ALW5rWFXrMb6I7VKukVh Aw8cYoECpdl6C8h1EHSX8h7ryZ+TbX5BAAfcVJLBiNBjaEsoGL4jNdbaKIBi/w5zzE8K SQ== Received: from phxpaimrmta01.imrmtpd1.prodappphxaev1.oraclevcn.com (phxpaimrmta01.appoci.oracle.com [138.1.114.2]) by mx0b-00069f02.pphosted.com (PPS) with ESMTPS id 3gbcauqfjn-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 01 Jun 2022 10:09:58 +0000 Received: from pps.filterd (phxpaimrmta01.imrmtpd1.prodappphxaev1.oraclevcn.com [127.0.0.1]) by phxpaimrmta01.imrmtpd1.prodappphxaev1.oraclevcn.com (8.16.1.2/8.16.1.2) with SMTP id 251A6Nig024485; Wed, 1 Jun 2022 10:09:58 GMT Received: from pps.reinject (localhost [127.0.0.1]) by phxpaimrmta01.imrmtpd1.prodappphxaev1.oraclevcn.com with ESMTP id 3gc8p3rg3t-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 01 Jun 2022 10:09:58 +0000 Received: from phxpaimrmta01.imrmtpd1.prodappphxaev1.oraclevcn.com (phxpaimrmta01.imrmtpd1.prodappphxaev1.oraclevcn.com [127.0.0.1]) by pps.reinject (8.16.0.36/8.16.0.36) with SMTP id 251A9vNJ030481; Wed, 1 Jun 2022 10:09:57 GMT Received: from t460.home (dhcp-10-175-24-90.vpn.oracle.com [10.175.24.90]) by phxpaimrmta01.imrmtpd1.prodappphxaev1.oraclevcn.com with ESMTP id 3gc8p3rg29-1; Wed, 01 Jun 2022 10:09:56 +0000 From: Vegard Nossum To: stable@vger.kernel.org Cc: Kees Cook , Ariadne Conill , Michael Kerrisk , Matthew Wilcox , Christian Brauner , Rich Felker , Eric Biederman , Alexander Viro , linux-fsdevel@vger.kernel.org, Andy Lutomirski , Vegard Nossum Subject: [PATCH 4.19.y] exec: Force single empty string when argv is empty Date: Wed, 1 Jun 2022 12:09:00 +0200 Message-Id: <20220601100900.1282-1-vegard.nossum@oracle.com> X-Mailer: git-send-email 2.35.1.46.g38062e73e0 In-Reply-To: <16489033844956@kroah.com> References: <16489033844956@kroah.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Proofpoint-ORIG-GUID: tQiVT8-6C5FjFr8HHlVbddVyEk8tYeEq X-Proofpoint-GUID: tQiVT8-6C5FjFr8HHlVbddVyEk8tYeEq Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Kees Cook commit dcd46d897adb70d63e025f175a00a89797d31a43 upstream. Quoting[1] Ariadne Conill: "In several other operating systems, it is a hard requirement that the second argument to execve(2) be the name of a program, thus prohibiting a scenario where argc < 1. POSIX 2017 also recommends this behaviour, but it is not an explicit requirement[2]: The argument arg0 should point to a filename string that is associated with the process being started by one of the exec functions. ... Interestingly, Michael Kerrisk opened an issue about this in 2008[3], but there was no consensus to support fixing this issue then. Hopefully now that CVE-2021-4034 shows practical exploitative use[4] of this bug in a shellcode, we can reconsider. This issue is being tracked in the KSPP issue tracker[5]." While the initial code searches[6][7] turned up what appeared to be mostly corner case tests, trying to that just reject argv == NULL (or an immediately terminated pointer list) quickly started tripping[8] existing userspace programs. The next best approach is forcing a single empty string into argv and adjusting argc to match. The number of programs depending on argc == 0 seems a smaller set than those calling execve with a NULL argv. Account for the additional stack space in bprm_stack_limits(). Inject an empty string when argc == 0 (and set argc = 1). Warn about the case so userspace has some notice about the change: process './argc0' launched './argc0' with NULL argv: empty string added Additionally WARN() and reject NULL argv usage for kernel threads. [1] https://lore.kernel.org/lkml/20220127000724.15106-1-ariadne@dereferenced.org/ [2] https://pubs.opengroup.org/onlinepubs/9699919799/functions/exec.html [3] https://bugzilla.kernel.org/show_bug.cgi?id=8408 [4] https://www.qualys.com/2022/01/25/cve-2021-4034/pwnkit.txt [5] https://github.com/KSPP/linux/issues/176 [6] https://codesearch.debian.net/search?q=execve%5C+*%5C%28%5B%5E%2C%5D%2B%2C+*NULL&literal=0 [7] https://codesearch.debian.net/search?q=execlp%3F%5Cs*%5C%28%5B%5E%2C%5D%2B%2C%5Cs*NULL&literal=0 [8] https://lore.kernel.org/lkml/20220131144352.GE16385@xsang-OptiPlex-9020/ Reported-by: Ariadne Conill Reported-by: Michael Kerrisk Cc: Matthew Wilcox Cc: Christian Brauner Cc: Rich Felker Cc: Eric Biederman Cc: Alexander Viro Cc: linux-fsdevel@vger.kernel.org Cc: stable@vger.kernel.org Signed-off-by: Kees Cook Acked-by: Christian Brauner Acked-by: Ariadne Conill Acked-by: Andy Lutomirski Link: https://lore.kernel.org/r/20220201000947.2453721-1-keescook@chromium.org [vegard: fixed conflicts due to missing 886d7de631da71e30909980fdbf318f7caade262^- and 3950e975431bc914f7e81b8f2a2dbdf2064acb0f^- and 655c16a8ce9c15842547f40ce23fd148aeccc074] Signed-off-by: Vegard Nossum --- fs/exec.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) This has been tested in both argc == 0 and argc >= 1 cases, but I would still appreciate a review given the differences with mainline. If it's considered too risky I'm also fine with dropping it -- just wanted to make sure this didn't fall through the cracks, as it does block a real (albeit old by now) exploit. diff --git a/fs/exec.c b/fs/exec.c index e87e3c020c61e..28e3b5eb2f4a1 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1805,6 +1805,9 @@ static int __do_execve_file(int fd, struct filename *filename, goto out_unmark; bprm->argc = count(argv, MAX_ARG_STRINGS); + if (bprm->argc == 0) + pr_warn_once("process '%s' launched '%s' with NULL argv: empty string added\n", + current->comm, bprm->filename); if ((retval = bprm->argc) < 0) goto out; @@ -1829,6 +1832,20 @@ static int __do_execve_file(int fd, struct filename *filename, if (retval < 0) goto out; + /* + * When argv is empty, add an empty string ("") as argv[0] to + * ensure confused userspace programs that start processing + * from argv[1] won't end up walking envp. See also + * bprm_stack_limits(). + */ + if (bprm->argc == 0) { + const char *argv[] = { "", NULL }; + retval = copy_strings_kernel(1, argv, bprm); + if (retval < 0) + goto out; + bprm->argc = 1; + } + retval = exec_binprm(bprm); if (retval < 0) goto out; -- 2.35.1.46.g38062e73e0