On Fri, Dec 22, 2017 at 4:14 AM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote: > On Thu, Dec 21, 2017 at 9:40 PM, Paul Moore <paul@xxxxxxxxxxxxxx> wrote: >> On Wed, Dec 20, 2017 at 2:48 AM, syzbot >> <bot+904436b33e141b4f4c57c1ddc94199ffd2e34b9d@xxxxxxxxxxxxxxxxxxxxxxxxx> >> 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. -- paul moore www.paul-moore.com
