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=-13.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 1660FC4338F for ; Mon, 23 Aug 2021 21:31:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E3ECC613D0 for ; Mon, 23 Aug 2021 21:31:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232920AbhHWVcS (ORCPT ); Mon, 23 Aug 2021 17:32:18 -0400 Received: from out02.mta.xmission.com ([166.70.13.232]:49614 "EHLO out02.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232748AbhHWVcQ (ORCPT ); Mon, 23 Aug 2021 17:32:16 -0400 Received: from in02.mta.xmission.com ([166.70.13.52]:45198) by out02.mta.xmission.com with esmtps (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1mIHXZ-007U4Y-7W; Mon, 23 Aug 2021 15:31:33 -0600 Received: from ip68-227-160-95.om.om.cox.net ([68.227.160.95]:37324 helo=email.xmission.com) by in02.mta.xmission.com with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1mIHXY-003d48-4S; Mon, 23 Aug 2021 15:31:32 -0600 From: ebiederm@xmission.com (Eric W. Biederman) To: Alexey Gladkov Cc: LKML , Linux Containers , syzbot+01985d7909f9468f013c@syzkaller.appspotmail.com References: <000000000000b1f4d305c9ef72ad@google.com> <97433b1742c3331f02ad92de5a4f07d673c90613.1629735352.git.legion@kernel.org> Date: Mon, 23 Aug 2021 16:31:25 -0500 In-Reply-To: <97433b1742c3331f02ad92de5a4f07d673c90613.1629735352.git.legion@kernel.org> (Alexey Gladkov's message of "Mon, 23 Aug 2021 18:16:33 +0200") Message-ID: <87tujfrgpe.fsf@disp2133> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-SPF: eid=1mIHXY-003d48-4S;;;mid=<87tujfrgpe.fsf@disp2133>;;;hst=in02.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX19pp4qrKf/JfCjQ/zA7PnEgzjip6wxQ7b8= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: [PATCH v1] ucounts: Increase ucounts reference counter before the security hook X-SA-Exim-Version: 4.2.1 (built Sat, 08 Feb 2020 21:53:50 +0000) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Alexey Gladkov writes: > We need to increment the ucounts reference counter befor security_prepare_creds() > because this function may fail and abort_creds() will try to decrement > this reference. > > [ 96.465056][ T8641] FAULT_INJECTION: forcing a failure. > [ 96.465056][ T8641] name fail_page_alloc, interval 1, probability 0, space 0, times 0 > [ 96.478453][ T8641] CPU: 1 PID: 8641 Comm: syz-executor668 Not tainted 5.14.0-rc6-syzkaller #0 > [ 96.487215][ T8641] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > [ 96.497254][ T8641] Call Trace: > [ 96.500517][ T8641] dump_stack_lvl+0x1d3/0x29f > [ 96.505758][ T8641] ? show_regs_print_info+0x12/0x12 > [ 96.510944][ T8641] ? log_buf_vmcoreinfo_setup+0x498/0x498 > [ 96.516652][ T8641] should_fail+0x384/0x4b0 > [ 96.521141][ T8641] prepare_alloc_pages+0x1d1/0x5a0 > [ 96.526236][ T8641] __alloc_pages+0x14d/0x5f0 > [ 96.530808][ T8641] ? __rmqueue_pcplist+0x2030/0x2030 > [ 96.536073][ T8641] ? lockdep_hardirqs_on_prepare+0x3e2/0x750 > [ 96.542056][ T8641] ? alloc_pages+0x3f3/0x500 > [ 96.546635][ T8641] allocate_slab+0xf1/0x540 > [ 96.551120][ T8641] ___slab_alloc+0x1cf/0x350 > [ 96.555689][ T8641] ? kzalloc+0x1d/0x30 > [ 96.559740][ T8641] __kmalloc+0x2e7/0x390 > [ 96.563980][ T8641] ? kzalloc+0x1d/0x30 > [ 96.568029][ T8641] kzalloc+0x1d/0x30 > [ 96.571903][ T8641] security_prepare_creds+0x46/0x220 > [ 96.577174][ T8641] prepare_creds+0x411/0x640 > [ 96.581747][ T8641] __sys_setfsuid+0xe2/0x3a0 > [ 96.586333][ T8641] do_syscall_64+0x3d/0xb0 > [ 96.590739][ T8641] entry_SYSCALL_64_after_hwframe+0x44/0xae > [ 96.596611][ T8641] RIP: 0033:0x445a69 > [ 96.600483][ T8641] Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 11 15 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48 > [ 96.620152][ T8641] RSP: 002b:00007f1054173318 EFLAGS: 00000246 ORIG_RAX: 000000000000007a > [ 96.628543][ T8641] RAX: ffffffffffffffda RBX: 00000000004ca4c8 RCX: 0000000000445a69 > [ 96.636600][ T8641] RDX: 0000000000000010 RSI: 00007f10541732f0 RDI: 0000000000000000 > [ 96.644550][ T8641] RBP: 00000000004ca4c0 R08: 0000000000000001 R09: 0000000000000000 > [ 96.652500][ T8641] R10: 0000000000000000 R11: 0000000000000246 R12: 00000000004ca4cc > [ 96.660631][ T8641] R13: 00007fffffe0b62f R14: 00007f1054173400 R15: 0000000000022000 > > Fixes: 905ae01c4ae2 ("Add a reference to ucounts for each cred") > Reported-by: syzbot+01985d7909f9468f013c@syzkaller.appspotmail.com > Signed-off-by: Alexey Gladkov Applied. It is obvious how a failure of security_prepare_creds calling abort_creds could result a decrement without an increment. So it looks like the fault injection did it's job. Eric > --- > kernel/cred.c | 12 ++++++------ > 1 file changed, 6 insertions(+), 6 deletions(-) > > diff --git a/kernel/cred.c b/kernel/cred.c > index e6fd2b3fc31f..f784e08c2fbd 100644 > --- a/kernel/cred.c > +++ b/kernel/cred.c > @@ -286,13 +286,13 @@ struct cred *prepare_creds(void) > new->security = NULL; > #endif > > - if (security_prepare_creds(new, old, GFP_KERNEL_ACCOUNT) < 0) > - goto error; > - > new->ucounts = get_ucounts(new->ucounts); > if (!new->ucounts) > goto error; > > + if (security_prepare_creds(new, old, GFP_KERNEL_ACCOUNT) < 0) > + goto error; > + > validate_creds(new); > return new; > > @@ -753,13 +753,13 @@ struct cred *prepare_kernel_cred(struct task_struct *daemon) > #ifdef CONFIG_SECURITY > new->security = NULL; > #endif > - if (security_prepare_creds(new, old, GFP_KERNEL_ACCOUNT) < 0) > - goto error; > - > new->ucounts = get_ucounts(new->ucounts); > if (!new->ucounts) > goto error; > > + if (security_prepare_creds(new, old, GFP_KERNEL_ACCOUNT) < 0) > + goto error; > + > put_cred(old); > validate_creds(new); > return new;