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 X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A56F3C43331 for ; Fri, 27 Mar 2020 00:51:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 819E620774 for ; Fri, 27 Mar 2020 00:51:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727787AbgC0Avs (ORCPT ); Thu, 26 Mar 2020 20:51:48 -0400 Received: from www262.sakura.ne.jp ([202.181.97.72]:50525 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727674AbgC0Avr (ORCPT ); Thu, 26 Mar 2020 20:51:47 -0400 Received: from fsav302.sakura.ne.jp (fsav302.sakura.ne.jp [153.120.85.133]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id 02R0pcVr011087; Fri, 27 Mar 2020 09:51:38 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav302.sakura.ne.jp (F-Secure/fsigk_smtp/550/fsav302.sakura.ne.jp); Fri, 27 Mar 2020 09:51:38 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/550/fsav302.sakura.ne.jp) Received: from [192.168.1.9] (M106072142033.v4.enabler.ne.jp [106.72.142.33]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id 02R0panf011076 (version=TLSv1.2 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Fri, 27 Mar 2020 09:51:37 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Subject: [PATCH (repost)] umh: fix refcount underflow in fork_usermode_blob(). From: Tetsuo Handa To: Andrew Morton Cc: Al Viro , linux-fsdevel , Alexei Starovoitov , "David S. Miller" References: <2a8775b4-1dd5-9d5c-aa42-9872445e0942@i-love.sakura.ne.jp> <20200312143801.GJ23230@ZenIV.linux.org.uk> <85163bf6-ae4a-edbb-6919-424b92eb72b2@i-love.sakura.ne.jp> Message-ID: <9b846b1f-a231-4f09-8c37-6bfb0d1e7b05@i-love.sakura.ne.jp> Date: Fri, 27 Mar 2020 09:51:34 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <85163bf6-ae4a-edbb-6919-424b92eb72b2@i-love.sakura.ne.jp> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Since free_bprm(bprm) always calls allow_write_access(bprm->file) and fput(bprm->file) if bprm->file is set to non-NULL, __do_execve_file() must call deny_write_access(file) and get_file(file) if called from do_execve_file() path. Otherwise, use-after-free access can happen at fput(file) in fork_usermode_blob(). general protection fault, probably for non-canonical address 0x6b6b6b6b6b6b6b6b: 0000 [#1] SMP DEBUG_PAGEALLOC CPU: 3 PID: 4131 Comm: insmod Tainted: G O 5.6.0-rc5+ #978 Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 07/29/2019 RIP: 0010:fork_usermode_blob+0xaa/0x190 Signed-off-by: Tetsuo Handa Fixes: 449325b52b7a6208 ("umh: introduce fork_usermode_blob() helper") Cc: [4.18+] Cc: Alexei Starovoitov Cc: David S. Miller Cc: Alexander Viro --- fs/exec.c | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index db17be51b112..ded3fa368dc7 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1761,11 +1761,17 @@ static int __do_execve_file(int fd, struct filename *filename, check_unsafe_exec(bprm); current->in_execve = 1; - if (!file) + if (!file) { file = do_open_execat(fd, filename, flags); - retval = PTR_ERR(file); - if (IS_ERR(file)) - goto out_unmark; + retval = PTR_ERR(file); + if (IS_ERR(file)) + goto out_unmark; + } else { + retval = deny_write_access(file); + if (retval) + goto out_unmark; + get_file(file); + } sched_exec(); -- 2.18.2