From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756514AbdLVQ7h (ORCPT ); Fri, 22 Dec 2017 11:59:37 -0500 Received: from mail-qk0-f195.google.com ([209.85.220.195]:44498 "EHLO mail-qk0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756298AbdLVQ7e (ORCPT ); Fri, 22 Dec 2017 11:59:34 -0500 X-Google-Smtp-Source: ACJfBotkdkn3ePyrzb1kNb3XxvGJI38g7NnhGApBMtKRLcAUu0Or5worXqCqAygxyhaadkQPSt2XxB/nM84AxWdn6gM= MIME-Version: 1.0 In-Reply-To: References: <94eb2c0d010a8dcf040560c0cdf5@google.com> From: Dmitry Vyukov Date: Fri, 22 Dec 2017 17:59:12 +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 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...