Re: BUG: unable to handle kernel NULL pointer dereference in sidtab_search_core

[Paul Moore]

On Fri, Dec 22, 2017 at 10:48 AM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
> On Fri, Dec 22, 2017 at 4:48 PM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> 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.
>>
>>
>> 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.
>
> Btw, this one I was able to reproduce with the syzbot provided
> reproducer in a second.
> It maybe doesn't make sense, but it's true.

FWIW, I ran the supplied reproducer for a few minutes yesterday and
didn't see a problem.  Your test kernels are based on linux-next, yes?

> [ 1768.418388] ==================================================================
> [ 1768.420222] kasan: CONFIG_KASAN_INLINE enabled
> [ 1768.420254] kasan: GPF could be caused by NULL-ptr deref or user
> memory access
> [ 1768.420283] general protection fault: 0000 [#1] SMP KASAN
> [ 1768.420290] Modules linked in:
> [ 1768.420309] CPU: 2 PID: 1705 Comm: kworker/u8:6 Not tainted 4.15.0-rc4+ #2
> [ 1768.420313] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
> BIOS Bochs 01/01/2011
> [ 1768.420363] RIP: 0010:sidtab_search_core+0x96/0x320
> [ 1768.420368] RSP: 0018:ffff8800644df6d8 EFLAGS: 00010a02
> [ 1768.420380] RAX: dffffc0000000000 RBX: c4c001a5000006a8 RCX: ffffffff82207e95
> [ 1768.420385] RDX: 18980034a00000d5 RSI: 0000000000000005 RDI: ffffffff874c29a0
> [ 1768.420391] RBP: ffff8800644df708 R08: 1ffff1000c89be25 R09: 0000000000000006
> [ 1768.420395] R10: ffff8800644df5f0 R11: 0000000000000000 R12: 0000000000000005
> [ 1768.420400] R13: 0000000000000005 R14: ffff880065e4db40 R15: ffff8800644df8a8
> [ 1768.420407] FS:  0000000000000000(0000) GS:ffff88006cd00000(0000)
> knlGS:0000000000000000
> [ 1768.420413] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 1768.420418] CR2: 0000000020269000 CR3: 0000000005e22003 CR4: 00000000001606e0
> [ 1768.420425] Call Trace:
> [ 1768.420443]  sidtab_search+0x1f/0x30
> [ 1768.420454]  security_compute_sid+0x31b/0x18f0
> [ 1768.420473]  ? security_context_to_sid_core+0x620/0x620
> [ 1768.420489]  ? __lock_is_held+0xb6/0x140
> [ 1768.420534]  ? ret_from_fork+0x24/0x30
> [ 1768.420552]  security_transition_sid+0x75/0x90
> [ 1768.420567]  selinux_bprm_set_creds+0x779/0xc20
> [ 1768.420582]  ? selinux_setprocattr+0xb50/0xb50
> [ 1768.420603]  ? debug_lockdep_rcu_enabled+0x77/0x90
> [ 1768.420617]  security_bprm_set_creds+0x6d/0xa0
> [ 1768.420635]  prepare_binprm+0x390/0x9f0
> [ 1768.420648]  ? install_exec_creds+0x170/0x170
> [ 1768.420657]  ? cpu_weight_nice_write_s64+0xd/0x80
> [ 1768.420672]  ? __might_fault+0x8e/0x1d0
> [ 1768.420684]  ? get_user_arg_ptr.isra.17+0x47/0xa0
> [ 1768.420711]  ? count.isra.19.constprop.32+0xbe/0x120
> [ 1768.420725]  do_execveat_common.isra.30+0x14b5/0x23c0
> [ 1768.420733]  ? save_stack+0xa3/0xd0
> [ 1768.420747]  ? path_openat+0x3510/0x3530
> [ 1768.420756]  ? ptregs_sys_rt_sigreturn+0x10/0x10
> [ 1768.420767]  ? prepare_bprm_creds+0x110/0x110
> [ 1768.420776]  ? check_noncircular+0x20/0x20
> [ 1768.420789]  ? find_held_lock+0x35/0x1d0
> [ 1768.420821]  ? trace_event_raw_event_sched_switch+0x800/0x800
> [ 1768.420831]  ? rcu_pm_notify+0xc0/0xc0
> [ 1768.420843]  ? getname_kernel+0x54/0x340
> [ 1768.420859]  ? rcu_read_lock_sched_held+0x108/0x120
> [ 1768.420871]  ? kmem_cache_alloc+0x466/0x760
> [ 1768.420881]  ? do_raw_spin_trylock+0x190/0x190
> [ 1768.420892]  ? get_task_cred+0x3b0/0x3b0
> [ 1768.420905]  do_execve+0x31/0x40
> [ 1768.420918]  call_usermodehelper_exec_async+0x457/0x8f0
> [ 1768.420926]  ? finish_task_switch+0x1d3/0x740
> [ 1768.420932]  ? finish_task_switch+0x1aa/0x740
> [ 1768.420941]  ? umh_complete+0x90/0x90
> [ 1768.420952]  ? copy_overflow+0x20/0x20
> [ 1768.420966]  ? umh_complete+0x90/0x90
> [ 1768.420975]  ? umh_complete+0x90/0x90
> [ 1768.420986]  ret_from_fork+0x24/0x30
> [ 1768.421011] Code: 3c 02 00 0f 85 41 02 00 00 48 8b 1b 48 85 db 0f
> 84 8b 00 00 00 e8 bb 6a 4f ff 48 89 da 48 b8 00 00 00 00 00 fc ff df
> 48 c1 ea 03 <0f> b6 04 02 84 c0 74 08 3c 03 0f 8e f4 01 00 00 44 8b 3b
> 45 39
> [ 1768.421166] RIP: sidtab_search_core+0x96/0x320 RSP: ffff8800644df6d8
> [ 1768.421279] ---[ end trace bfed1c399df72093 ]---
> [ 1768.421285] Kernel panic - not syncing: Fatal exception
> [ 1768.486255] BUG: KASAN: use-after-free in sidtab_search_core+0x2bd/0x320
> [ 1768.487474] Read of size 8 at addr ffff880065e4db48 by task id/1702
> [ 1768.488619]
> [ 1768.488914] CPU: 1 PID: 1702 Comm: id Tainted: G      D
> 4.15.0-rc4+ #2
> [ 1768.490264] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
> BIOS Bochs 01/01/2011
> [ 1768.491718] Call Trace:
> [ 1768.492193]  dump_stack+0x194/0x257
> [ 1768.492849]  ? arch_local_irq_restore+0x53/0x53
> [ 1768.493709]  ? show_regs_print_info+0x18/0x18
> [ 1768.494431]  ? lock_acquire+0x1d5/0x580
> [ 1768.495079]  ? sidtab_search_core+0x2bd/0x320
> [ 1768.495894]  print_address_description+0x73/0x250
> [ 1768.496707]  ? sidtab_search_core+0x2bd/0x320
> [ 1768.497481]  kasan_report+0x25b/0x340
> [ 1768.498136]  __asan_report_load8_noabort+0x14/0x20
> [ 1768.498962]  sidtab_search_core+0x2bd/0x320
> [ 1768.499702]  sidtab_search+0x1f/0x30
> [ 1768.500344]  security_sid_mls_copy+0x1cf/0xa30
> [ 1768.501123]  ? security_get_bool_value+0xb0/0xb0
> [ 1768.501934]  ? avc_has_perm+0x43e/0x680
> [ 1768.502602]  ? avc_has_perm_noaudit+0x520/0x520
> [ 1768.503385]  ? lock_release+0xa40/0xa40
> [ 1768.504052]  ? lock_downgrade+0x980/0x980
> [ 1768.504751]  ? do_raw_spin_unlock+0x1ec/0x300
> [ 1768.505625]  ? mnt_get_count+0x150/0x150
> [ 1768.506298]  ? dput.part.23+0x207/0x830
> [ 1768.506938]  selinux_socket_unix_stream_connect+0x364/0x590
> [ 1768.507853]  ? lock_acquire+0x1d5/0x580
> [ 1768.508495]  ? lock_acquire+0x1d5/0x580
> [ 1768.509138]  ? selinux_inet_conn_request+0x390/0x390
> [ 1768.509972]  ? lock_release+0xa40/0xa40
> [ 1768.510634]  ? unix_bind+0xf90/0xf90
> [ 1768.511246]  security_unix_stream_connect+0x7d/0xb0
> [ 1768.512066]  unix_stream_connect+0x8bc/0x1580
> [ 1768.512824]  ? unix_release+0x90/0x90
> [ 1768.513446]  ? __might_sleep+0x95/0x190
> [ 1768.514101]  ? security_socket_connect+0x89/0xb0
> [ 1768.514880]  SYSC_connect+0x213/0x4a0
> [ 1768.515589]  ? SYSC_bind+0x410/0x410
> [ 1768.516193]  ? get_unused_fd_flags+0x121/0x190
> [ 1768.516944]  ? entry_SYSCALL_64_fastpath+0x5/0x96
> [ 1768.517736]  ? trace_hardirqs_on_caller+0x421/0x5c0
> [ 1768.518531]  SyS_connect+0x24/0x30
> [ 1768.519081]  entry_SYSCALL_64_fastpath+0x1f/0x96
> [ 1768.519820] RIP: 0033:0x7f0bbb592fd0
> [ 1768.520392] RSP: 002b:00007ffe7688aed8 EFLAGS: 00000246 ORIG_RAX:
> 000000000000002a
> [ 1768.521574] RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f0bbb592fd0
> [ 1768.522678] RDX: 000000000000006e RSI: 00007ffe7688aee0 RDI: 0000000000000003
> [ 1768.523788] RBP: 0000000000608260 R08: 0000000000000004 R09: 000000000064d010
> [ 1768.524896] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
> [ 1768.526080] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000001
> [ 1768.527182]
> [ 1768.527439] Allocated by task 1:
> [ 1768.527961]  save_stack+0x43/0xd0
> [ 1768.528492]  kasan_kmalloc+0xad/0xe0
> [ 1768.529061]  kmem_cache_alloc_trace+0x136/0x750
> [ 1768.529791]  sidtab_init+0x4b/0x1c0
> [ 1768.530346]  policydb_load_isids+0x20/0x220
> [ 1768.531043]  security_load_policy+0x5c1/0x1260
> [ 1768.531790]  sel_write_load+0x241/0x1910
> [ 1768.532447]  __vfs_write+0xef/0x970
> [ 1768.533035]  vfs_write+0x189/0x510
> [ 1768.533613]  SyS_write+0xef/0x220
> [ 1768.534167]  entry_SYSCALL_64_fastpath+0x1f/0x96
> [ 1768.534891]
> [ 1768.535141] Freed by task 0:
> [ 1768.535695] (stack is not available)
> [ 1768.536266]
> [ 1768.536521] The buggy address belongs to the object at ffff880065e4db40
> [ 1768.536521]  which belongs to the cache kmalloc-1024 of size 1024
> [ 1768.538504] The buggy address is located 8 bytes inside of
> [ 1768.538504]  1024-byte region [ffff880065e4db40, ffff880065e4df40)
> [ 1768.540296] The buggy address belongs to the page:
> [ 1768.541057] page:00000000221ddb34 count:1 mapcount:0
> mapping:00000000c8b57d81 index:0x0 compound_mapcount: 0
> [ 1768.542565] flags: 0x1fffc0000008100(slab|head)
> [ 1768.543261] raw: 01fffc0000008100 ffff880065e4c040 0000000000000000
> 0000000100000007
> [ 1768.544419] raw: ffffea0001b0fba0 ffffea0001aa1920 ffff88006c800ac0
> 0000000000000000
> [ 1768.545595] page dumped because: kasan: bad access detected
> [ 1768.546497]
> [ 1768.546741] Memory state around the buggy address:
> [ 1768.547469]  ffff880065e4da00: fb fb fb fb fb fb fb fb fb fb fb fb
> fb fb fb fb
> [ 1768.548554]  ffff880065e4da80: fb fb fb fb fb fb fb fb fb fb fb fb
> fb fb fb fb
> [ 1768.549679] >ffff880065e4db00: fb fb fb fb fb fb fb fb fb fb fb fb
> 00 00 00 00
> [ 1768.550737]                                               ^
> [ 1768.551565]  ffff880065e4db80: 00 00 00 00 00 00 00 00 00 00 00 00
> 00 00 00 00
> [ 1768.552627]  ffff880065e4dc00: 00 00 00 00 00 00 00 00 00 00 00 00
> 00 00 00 00
> [ 1768.553694] ==================================================================
> [ 1768.554780] Kernel Offset: disabled
> [ 1768.555312] Rebooting in 86400 seconds..



-- 
paul moore
www.paul-moore.com