From patchwork Fri May 8 18:47:10 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Eric W. Biederman" X-Patchwork-Id: 11537447 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 9909814B4 for ; Fri, 8 May 2020 18:50:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8AEA8218AC for ; Fri, 8 May 2020 18:50:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727083AbgEHSuj (ORCPT ); Fri, 8 May 2020 14:50:39 -0400 Received: from out01.mta.xmission.com ([166.70.13.231]:54972 "EHLO out01.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726767AbgEHSuj (ORCPT ); Fri, 8 May 2020 14:50:39 -0400 Received: from in01.mta.xmission.com ([166.70.13.51]) by out01.mta.xmission.com with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1jX84z-0005ZA-W0; Fri, 08 May 2020 12:50:38 -0600 Received: from ip68-227-160-95.om.om.cox.net ([68.227.160.95] helo=x220.xmission.com) by in01.mta.xmission.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.87) (envelope-from ) id 1jX84z-0003BB-7i; Fri, 08 May 2020 12:50:37 -0600 From: ebiederm@xmission.com (Eric W. Biederman) To: Cc: Linus Torvalds , Oleg Nesterov , Jann Horn , Kees Cook , Greg Ungerer , Rob Landley , Bernd Edlinger , , Al Viro , Alexey Dobriyan , Andrew Morton References: <87h7wujhmz.fsf@x220.int.ebiederm.org> <87sgga6ze4.fsf@x220.int.ebiederm.org> Date: Fri, 08 May 2020 13:47:10 -0500 In-Reply-To: <87sgga6ze4.fsf@x220.int.ebiederm.org> (Eric W. Biederman's message of "Fri, 08 May 2020 13:43:31 -0500") Message-ID: <87y2q25knl.fsf_-_@x220.int.ebiederm.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 X-XM-SPF: eid=1jX84z-0003BB-7i;;;mid=<87y2q25knl.fsf_-_@x220.int.ebiederm.org>;;;hst=in01.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX1+FnkFDblASDXzpBgep8n0qUcQ6c8wP+Zg= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on sa05.xmission.com X-Spam-Level: ** X-Spam-Status: No, score=2.0 required=8.0 tests=ALL_TRUSTED,BAYES_50, DCC_CHECK_NEGATIVE,XMNoVowels,XMSubLong autolearn=disabled version=3.4.2 X-Spam-Report: * -1.0 ALL_TRUSTED Passed through trusted hosts only via SMTP * 0.8 BAYES_50 BODY: Bayes spam probability is 40 to 60% * [score: 0.5000] * 1.5 XMNoVowels Alpha-numberic number with no vowels * 0.7 XMSubLong Long Subject * -0.0 DCC_CHECK_NEGATIVE Not listed in DCC * [sa05 0; Body=1 Fuz1=1 Fuz2=1] X-Spam-DCC: ; sa05 0; Body=1 Fuz1=1 Fuz2=1 X-Spam-Combo: **; X-Spam-Relay-Country: X-Spam-Timing: total 435 ms - load_scoreonly_sql: 0.11 (0.0%), signal_user_changed: 14 (3.1%), b_tie_ro: 11 (2.6%), parse: 1.85 (0.4%), extract_message_metadata: 19 (4.5%), get_uri_detail_list: 2.7 (0.6%), tests_pri_-1000: 21 (4.7%), tests_pri_-950: 1.81 (0.4%), tests_pri_-900: 1.48 (0.3%), tests_pri_-90: 65 (14.9%), check_bayes: 62 (14.4%), b_tokenize: 10 (2.3%), b_tok_get_all: 8 (1.9%), b_comp_prob: 2.9 (0.7%), b_tok_touch_all: 38 (8.8%), b_finish: 0.97 (0.2%), tests_pri_0: 284 (65.2%), check_dkim_signature: 0.90 (0.2%), check_dkim_adsp: 3.0 (0.7%), poll_dns_idle: 0.55 (0.1%), tests_pri_10: 4.4 (1.0%), tests_pri_500: 18 (4.2%), rewrite_mail: 0.00 (0.0%) Subject: [PATCH 5/6] exec: Move handling of the point of no return to the top level X-Spam-Flag: No X-SA-Exim-Version: 4.2.1 (built Thu, 05 May 2016 13:38:54 -0600) X-SA-Exim-Scanned: Yes (on in01.mta.xmission.com) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Move the handing of the point of no return from search_binary_handler into __do_execve_file so that it is easier to find, and to keep things robust in the face of change. Make it clear that an existing fatal signal will take precedence over a forced SIGSEGV by not forcing SIGSEGV if a fatal signal is already pending. This does not change the behavior but it saves a reader of the code the tedium of reading and understanding force_sig and the signal delivery code. Update the comment in begin_new_exec about where SIGSEGV is forced. Keep point_of_no_return from being a mystery by documenting what the code is doing where it forces SIGSEGV if the code is past the point of no return. Signed-off-by: "Eric W. Biederman" Reviewed-by: Kees Cook --- fs/exec.c | 21 ++++++++++++--------- 1 file changed, 12 insertions(+), 9 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index 15682a1dfee9..443eb960f9a0 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1329,8 +1329,8 @@ int begin_new_exec(struct linux_binprm * bprm) /* * With the new mm installed it is completely impossible to * fail and return to the original process. If anything from - * here on returns an error, the check in - * search_binary_handler() will SEGV current. + * here on returns an error, the check in __do_execve_file() + * will SEGV current. */ bprm->point_of_no_return = true; bprm->mm = NULL; @@ -1722,13 +1722,8 @@ int search_binary_handler(struct linux_binprm *bprm) read_lock(&binfmt_lock); put_binfmt(fmt); - if (retval < 0 && bprm->point_of_no_return) { - /* we got to flush_old_exec() and failed after it */ - read_unlock(&binfmt_lock); - force_sigsegv(SIGSEGV); - return retval; - } - if (retval != -ENOEXEC || !bprm->file) { + if (bprm->point_of_no_return || !bprm->file || + (retval != -ENOEXEC)) { read_unlock(&binfmt_lock); return retval; } @@ -1899,6 +1894,14 @@ static int __do_execve_file(int fd, struct filename *filename, return retval; out: + /* + * If past the point of no return ensure the the code never + * returns to the userspace process. Use an existing fatal + * signal if present otherwise terminate the process with + * SIGSEGV. + */ + if (bprm->point_of_no_return && !fatal_signal_pending(current)) + force_sigsegv(SIGSEGV); if (bprm->mm) { acct_arg_size(bprm, 0); mmput(bprm->mm);