From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756824AbdLVU4k (ORCPT ); Fri, 22 Dec 2017 15:56:40 -0500 Received: from mail-lf0-f66.google.com ([209.85.215.66]:37216 "EHLO mail-lf0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756682AbdLVU4h (ORCPT ); Fri, 22 Dec 2017 15:56:37 -0500 X-Google-Smtp-Source: ACJfBovHwxXFkXBdf6NZbKfq15Va0XnDAp1qQOGCsu8aW1SXJIr2PA1oyn87wRQmUVjUs1Ax9GEdbSIWInKr4Pv9D/Q= MIME-Version: 1.0 X-Originating-IP: [108.20.156.165] In-Reply-To: References: <94eb2c0d010a8dcf040560c0cdf5@google.com> From: Paul Moore Date: Fri, 22 Dec 2017 15:56:34 -0500 Message-ID: Subject: Re: BUG: unable to handle kernel NULL pointer dereference in sidtab_search_core To: Dmitry Vyukov 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 Fri, Dec 22, 2017 at 11:59 AM, Dmitry Vyukov wrote: > On Fri, Dec 22, 2017 at 5:03 PM, Paul Moore wrote: >>>>>> 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. >>>> >>>> I've replied to several of the syzbot automated reports with the >>>> "invalid" response. I haven't been keeping track, but it seems like >>>> approximately 50% of the SELinux related reports don't make sense upon >>>> inspection. >>> >>> Can you please point me to some of these bugs? I don't see anything >>> like this in my inbox, in google group nor in database. >> >> Not easily, no. I don't keep track of these reports once I've >> responded to the syzbot mail. > > There must be traces of this in database and on mailing lists (even if > you drop syzkaller-bugs@ syzbot will re-add it). So far I did not find > any traces... Okay, so I dug through my mail and I found at least two instances (see below). There may be more, but I'm getting tired of dealing with syzbot. I'm a big fan of increased testing, especially automated testing, but right now syzbot seems to be costing me a disproportionate amount of time. * I sent an invalid reply to bot+c06fb26dfcd8220259619bf322a79eb0887147c8 on November 3rd, I don't see an acknowledgement from the robot but I may have deleted it. * I sent an invalid reply to bot+fcb30800d359ef1113a6edda069a77c2eebb9bf1 on December 6th, it was acknowledged by the robot. -- paul moore www.paul-moore.com