From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965488AbdLVJPe (ORCPT ); Fri, 22 Dec 2017 04:15:34 -0500 Received: from mail-pl0-f66.google.com ([209.85.160.66]:41213 "EHLO mail-pl0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933498AbdLVJPK (ORCPT ); Fri, 22 Dec 2017 04:15:10 -0500 X-Google-Smtp-Source: ACJfBosb4jvZFjOgxQMzQTj+gPz8nCm62xoWXQdUxT8SqNZzNgphVab44HTzD7BkqK+6mcWzWYBccfhhocdFzHc+IJI= MIME-Version: 1.0 In-Reply-To: References: <94eb2c0d010a8dcf040560c0cdf5@google.com> From: Dmitry Vyukov Date: Fri, 22 Dec 2017 10:14:48 +0100 Message-ID: Subject: Re: BUG: unable to handle kernel NULL pointer dereference in sidtab_search_core To: Paul Moore Cc: syzbot , elfring@users.sourceforge.net, Eric Paris , Greg Kroah-Hartman , James Morris , LKML , linux-security-module@vger.kernel.org, Philippe Ombredanne , Stephen Smalley , selinux@tycho.nsa.gov, serge@hallyn.com, syzkaller-bugs@googlegroups.com, Thomas Gleixner Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Dec 21, 2017 at 9:40 PM, Paul Moore wrote: > On Wed, Dec 20, 2017 at 2:48 AM, syzbot > > wrote: >> Hello, >> >> syzkaller hit the following crash on >> 6084b576dca2e898f5c101baef151f7bfdbb606d >> git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/master >> compiler: gcc (GCC) 7.1.1 20170620 >> .config is attached >> Raw console output is attached. >> C reproducer is attached >> syzkaller reproducer is attached. See https://goo.gl/kgGztJ >> for information about syzkaller reproducers >> >> >> SELinux: security_compute_sid: unrecognized SID 1 >> SELinux: security_compute_sid: unrecognized SID 1 >> SELinux: security_compute_sid: unrecognized SID 1 >> SELinux: security_compute_sid: unrecognized SID 1 >> SELinux: security_compute_sid: unrecognized SID 1 >> BUG: unable to handle kernel NULL pointer dereference at 0000000000000001 >> IP: sidtab_search_core+0x88/0x110 security/selinux/ss/sidtab.c:100 >> PGD 0 P4D 0 >> Oops: 0000 [#1] SMP >> Dumping ftrace buffer: >> (ftrace buffer empty) >> Modules linked in: >> CPU: 1 PID: 4252 Comm: kworker/u4:1 Not tainted 4.15.0-rc3-next-20171214+ >> #67 >> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS >> Google 01/01/2011 >> RIP: 0010:sidtab_search_core+0x88/0x110 security/selinux/ss/sidtab.c:100 >> RSP: 0018:ffffc900028abc18 EFLAGS: 00010293 >> RAX: ffff8802131a87c0 RBX: 0000000000000001 RCX: ffffffff8165d978 >> RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffffffff83fd17a0 >> RBP: ffffc900028abc40 R08: 0000000000000001 R09: 0000000000000001 >> R10: ffffc900028abbe0 R11: 0000000000000000 R12: 0000000000000001 >> R13: 0000000000000001 R14: 0000000000000000 R15: ffff880214d93800 >> FS: 0000000000000000(0000) GS:ffff88021fd00000(0000) knlGS:0000000000000000 >> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >> CR2: 0000000000000001 CR3: 0000000214e31000 CR4: 00000000001406e0 >> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 >> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 >> Call Trace: >> sidtab_search+0x1f/0x30 security/selinux/ss/sidtab.c:111 >> security_compute_sid.part.11+0xe2/0x710 security/selinux/ss/services.c:1618 >> security_compute_sid+0x92/0xa0 security/selinux/ss/services.c:1598 >> security_transition_sid+0x57/0x70 security/selinux/ss/services.c:1764 >> selinux_bprm_set_creds+0x215/0x2f0 security/selinux/hooks.c:2423 >> security_bprm_set_creds+0x41/0x60 security/security.c:332 >> prepare_binprm+0xae/0x1f0 fs/exec.c:1561 >> do_execveat_common.isra.30+0x6f7/0xb90 fs/exec.c:1784 >> do_execve+0x31/0x40 fs/exec.c:1848 >> call_usermodehelper_exec_async+0x104/0x190 kernel/umh.c:100 >> ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:524 >> Code: 8b 5b 50 48 85 db 75 e5 e8 e6 c9 c5 ff 49 8b 5f 18 48 85 db 75 10 eb >> 43 e8 d6 c9 c5 ff 48 8b 5b 50 48 85 db 74 35 e8 c8 c9 c5 ff <44> 8b 23 41 83 >> fc 02 76 e4 e8 ba c9 c5 ff 41 83 fc 03 75 1c 48 >> RIP: sidtab_search_core+0x88/0x110 security/selinux/ss/sidtab.c:100 RSP: >> ffffc900028abc18 >> CR2: 0000000000000001 >> ---[ end trace 571c0ea6c6959387 ]--- >> Kernel panic - not syncing: Fatal exception >> Dumping ftrace buffer: >> (ftrace buffer empty) >> Kernel Offset: disabled >> Rebooting in 86400 seconds.. > > Based on the reproducer and the stack trace, I'm guessing the system > is attempting to load a kernel module for a a defined, but unloaded, > protocol. Looking quickly at the SELinux bprm and sidtab code, > nothing obvious is jumping out at me. Considering the number of false > positives I've been seeing from syzbot lately, I'm assuming this is > more of the same. Hi Paul, What are these false positives? Please elaborate. There is no single false positive that I am aware of. All the ones that were debugged are real kernel bugs.