Re: general protection fault in show_timer

[Dmitry Vyukov]

+syzbot back, please don't drop it, it's reading


On Thu, Nov 30, 2017 at 1:20 PM, Alexey Dobriyan <adobriyan@xxxxxxxxx> wrote:
> [cc security@]
> 100% oops with interrupts disabled by nobody
> or kernel memory read
>
>
> On 11/30/17, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
>> On Thu, Nov 30, 2017 at 12:31 PM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
>>> On Thu, Nov 30, 2017 at 12:08 PM, Alexey Dobriyan <adobriyan@xxxxxxxxx>
>>> wrote:
>>>> On 11/30/17, syzbot
>>>> <bot+054c6cd125793643a90db21e4b9ddc71a881f797@xxxxxxxxxxxxxxxxxxxxxxxxx>
>>>> wrote:
>>>>> Hello,
>>>>>
>>>>> syzkaller hit the following crash on
>>>>> 43570f0383d6d5879ae585e6c3cf027ba321546f
>>>>> git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/master
>>>>> compiler: gcc (GCC) 7.1.1 20170620
>>>>> .config is attached
>>>>> Raw console output is attached.
>>>>>
>>>>> Unfortunately, I don't have any reproducer for this bug yet.
>>>>>
>>>>>
>>>>> kasan: CONFIG_KASAN_INLINE enabled
>>>>> kasan: GPF could be caused by NULL-ptr deref or user memory access
>>>>> general protection fault: 0000 [#1] SMP KASAN
>>>>> Dumping ftrace buffer:
>>>>>     (ftrace buffer empty)
>>>>> Modules linked in:
>>>>> CPU: 1 PID: 22618 Comm: syz-executor4 Not tainted 4.15.0-rc1+ #199
>>>>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
>>>>> Google 01/01/2011
>>>>> task: ffff8801c048c400 task.stack: ffff8801cd968000
>>>>> RIP: 0010:show_timer+0x1c7/0x2b0 fs/proc/base.c:2274
>>>>> RSP: 0018:ffff8801cd96f9e0 EFLAGS: 00010006
>>>>> RAX: dffffc0000000000 RBX: ffff8801cff22e40 RCX: ffffffff81ccb88e
>>>>> RDX: 0000000030a68524 RSI: ffffc90002dea000 RDI: 0000000185342920
>>>>> RBP: ffff8801cd96fa10 R08: ffffed003a0514c5 R09: ffffed003a0514c5
>>>>> R10: ffff8801c048c400 R11: ffffed003a0514c4 R12: 0000000040000000
>>>>> R13: ffff8801c79e7000 R14: ffffffff853419e0 R15: 0000000000000507
>>>>> FS:  00007f19f811e700(0000) GS:ffff8801db500000(0000)
>>>>> knlGS:0000000000000000
>>>>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>>>> CR2: 00007f4ab586bdb8 CR3: 00000001d1788000 CR4: 00000000001426e0
>>>>> DR0: 0000000020000000 DR1: 0000000020000008 DR2: 0000000000000000
>>>>> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000600
>>>>> Call Trace:
>>>>>   traverse+0x248/0xa00 fs/seq_file.c:111
>>>>>   seq_read+0x96a/0x13d0 fs/seq_file.c:189
>>>>>   do_loop_readv_writev fs/read_write.c:673 [inline]
>>>>>   do_iter_read+0x3db/0x5b0 fs/read_write.c:897
>>>>>   vfs_readv+0x121/0x1c0 fs/read_write.c:959
>>>>>   do_preadv+0x11b/0x1a0 fs/read_write.c:1043
>>>>>   SYSC_preadv fs/read_write.c:1093 [inline]
>>>>>   SyS_preadv+0x30/0x40 fs/read_write.c:1088
>>>>>   entry_SYSCALL_64_fastpath+0x1f/0x96
>>>>> RIP: 0033:0x4529d9
>>>>> RSP: 002b:00007f19f811dc58 EFLAGS: 00000212 ORIG_RAX: 0000000000000127
>>>>> RAX: ffffffffffffffda RBX: 00007f19f811d950 RCX: 00000000004529d9
>>>>> RDX: 0000000000000001 RSI: 00000000205e2ff0 RDI: 0000000000000013
>>>>> RBP: 00007f19f811d940 R08: 0000000000000000 R09: 0000000000000000
>>>>> R10: 0001000000000000 R11: 0000000000000212 R12: 00000000004b7346
>>>>> R13: 00007f19f811dac8 R14: 00000000004b7351 R15: 0000000000000000
>>>>> Code: 89 c7 4c 0f 44 f1 41 83 e4 fb 4d 63 e4 e8 a2 2f a3 ff 4a 8d 3c e5
>>>>> 20
>>>>>
>>>>> 29 34 85 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02
>>>>> 00
>>>>> 0f 85 a2 00 00 00 4a 8b 14 e5 20 29 34 85 4c 89 ef
>>>>> RIP: show_timer+0x1c7/0x2b0 fs/proc/base.c:2274 RSP: ffff8801cd96f9e0
>>>>
>>>> This looks like ASAN problem
>>>>
>>>> ffffffff81a5f1d9:       e8 72 74 b7 ff          call
>>>> ffffffff815d6650 <__sanitizer_cov_trace_pc>
>>>> ffffffff81a5f1de:       4a 8d 3c e5 a0 9e b4    lea
>>>> rdi,[r12*8-0x7b4b6160]
>>>> ffffffff81a5f1e5:       84
>>>> ffffffff81a5f1e6:       48 b8 00 00 00 00 00    movabs
>>>> rax,0xdffffc0000000000
>>>> ffffffff81a5f1ed:       fc ff df
>>>> ffffffff81a5f1f0:       48 89 fa                mov    rdx,rdi
>>>> ffffffff81a5f1f3:       48 c1 ea 03             shr    rdx,0x3
>>>> ffffffff81a5f1f7:       80 3c 02 00     ===>cmp    BYTE PTR
>>>> [rdx+rax*1],0x0  <====
>>>>
>>>> This is code injected by KASAN_INLINE
>>>>
>>>> timer_show() looks seemingly fine:
>>>> "timer" pointer is valid otherwise code would oopsed earlier
>>>> tp->ns is valid otherwise it'd oopsed inside pid_nr_ns()
>>>
>>>
>>> This is not KASAN bug. Kernel tries to dereference 0x0000000185342920.
>>> Failure mode is just different.
>
> I'm new to KASAN.
>
>> it seems that notify is equal to 0x0000000040000000 and this makes
>> nstr[notify & ~SIGEV_THREAD_ID] a totally wild access.
>
> [nods]
> you named the bug already
>
> "notify" directly comes from userspace struct sigevent::sigev_notify
> without adult supervision.
>
> Reproducer is timer_create + read(/proc/self/timers)
>
> BUG: unable to handle kernel paging request at 00000000b3695f68
> IP: show_timer+0x73/0xa0
> PGD 3d18f067 P4D 3d18f067 PUD 0
> Oops: 0000 [#1] PREEMPT SMP
> CPU: 0 PID: 2819 Comm: a.out Not tainted 4.15.0-rc1-00179-ga0908a1b7d68 #2
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> 1.10.2-1.fc27 04/01/2014
> task: 00000000ea51a5c5 task.stack: 00000000d68c2dbc
> RIP: 0010:show_timer+0x73/0xa0
> RSP: 0018:ffffc900001bfdd0 EFLAGS: 00010006
> RAX: ffffffff814cddbd RBX: 0000000040000000 RCX: ffffffff814cddbd
> RDX: 0000000000000000 RSI: ffffffff814d9419 RDI: ffff88003dab9500
> RBP: ffff88003dab9500 R08: 0000000000000b03 R09: 0000000000000007
> R10: ffffc9000040b908 R11: ffff88003d9ce020 R12: ffff88003c1c6570
> R13: ffff88003d514d80 R14: ffff88003dab9500 R15: ffff88003c1c6570
> FS:  00007f52624f0700(0000) GS:ffff88003fc00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000181414880 CR3: 000000003c243000 CR4: 00000000000006b0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  seq_read+0xe6/0x3b0
>  __vfs_read+0x1e/0x120
>  ? ptrace_do_notify+0x6a/0x80
>  vfs_read+0x84/0x110
>  SyS_read+0x3d/0xa0
>  do_syscall_64+0x4b/0x180
>  entry_SYSCALL64_slow_path+0x25/0x25
> RIP: 0033:0x7f5261e15fc0
> RSP: 002b:00007ffd2f89f5c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f5261e15fc0
> RDX: 0000000000001000 RSI: 00007ffd2f89f620 RDI: 0000000000000003
> RBP: 0000000000000000 R08: 00007f52620cce40 R09: 00007f5261d47c60
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000400574
> R13: 00007ffd2f8a0700 R14: 0000000000000000 R15: 0000000000000000
> Code: 89 f1 ff f6 c3 04 48 89 ef 48 c7 c1 c9 44 4c 81 41 89 c0 48 c7
> c0 bd dd 4c 81 48 c7 c6 19 94 4d 81 48 0f 44 c8 83 e3 fb 48 63 db <48>
> 8b 14 dd 80 48 41 81 e8 f0 3b fd ff 41 8b 54 24 30 48 89 ef
> RIP: show_timer+0x73/0xa0 RSP: ffffc900001bfdd0
> CR2: 0000000181414880
> ---[ end trace 99049f704e3a24ad ]---
> note: a.out[2819] exited with preempt_count 1