Re: general protection fault in proc_flush_task

[Eric Biggers]

On Wed, Nov 29, 2017 at 10:23:00PM -0800, syzbot wrote:
> Hello,
> 
> syzkaller hit the following crash on
> 0c86a6bd85ff0629cd2c5141027fc1c8bb6cde9c
> git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next.git/master
> compiler: gcc (GCC) 7.1.1 20170620
> .config is attached
> Raw console output is attached.
> 
> syzkaller reproducer is attached. See https://goo.gl/kgGztJ
> for information about syzkaller reproducers
> 
> 
> 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: 0 PID: 3163 Comm: syz-executor1 Not tainted 4.14.0+ #190
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> task: ffff8801cbcfa440 task.stack: ffff8801cbc70000
> RIP: 0010:proc_flush_task_mnt fs/proc/base.c:3028 [inline]
> RIP: 0010:proc_flush_task+0x26d/0x6c0 fs/proc/base.c:3100
> RSP: 0018:ffff8801cbc77408 EFLAGS: 00010246
> RAX: 0000000000000000 RBX: dffffc0000000000 RCX: ffffed003978ee95
> RDX: 0000000000000000 RSI: dffffc0000000000 RDI: 1ffff1003978ee53
> RBP: ffff8801cbc77510 R08: 0000000000000000 R09: 1ffff1003978ee0c
> R10: 0000000000000500 R11: 0000000000000000 R12: ffff8801cbc774a8
> R13: 0000000000000000 R14: ffff8801c87fce80 R15: ffff8801cbc77468
> FS:  00000000012dc940(0000) GS:ffff8801db400000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00000000208e5ff0 CR3: 00000001cbed4000 CR4: 00000000001406f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  release_task+0x258/0x1a40 kernel/exit.c:195
>  wait_task_zombie kernel/exit.c:1161 [inline]
>  wait_consider_task+0x2a10/0x3420 kernel/exit.c:1388
>  do_wait_thread kernel/exit.c:1451 [inline]
>  do_wait+0x427/0xa70 kernel/exit.c:1522
>  kernel_wait4+0x1f5/0x370 kernel/exit.c:1665
>  SYSC_wait4+0x134/0x140 kernel/exit.c:1677
>  SyS_wait4+0x2c/0x40 kernel/exit.c:1673
>  entry_SYSCALL_64_fastpath+0x1f/0x96
> RIP: 0033:0x40cbfa
> RSP: 002b:0000000000a6fa28 EFLAGS: 00000246 ORIG_RAX: 000000000000003d
> RAX: ffffffffffffffda RBX: 00000000012dc914 RCX: 000000000040cbfa
> RDX: 0000000040000001 RSI: 0000000000a6fa4c RDI: ffffffffffffffff
> RBP: 0000000000000086 R08: 0000000000000001 R09: 00000000012dc940
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 000000000000000a R14: 00000000001a0347 R15: 0000000000000016
> Code: 7d a0 e8 17 2c 43 03 48 8b 8d 10 ff ff ff 0f b6 11 38 95 33 ff ff ff
> 7c 08 84 d2 0f 85 73 03 00 00 89 45 9c 4c 89 e8 48 c1 e8 03 <80> 3c 18 00 0f
> 85 52 03 00 00 49 8b 7d 00 4c 89 e6 e8 8d 93 e7
> RIP: proc_flush_task_mnt fs/proc/base.c:3028 [inline] RSP: ffff8801cbc77408
> RIP: proc_flush_task+0x26d/0x6c0 fs/proc/base.c:3100 RSP: ffff8801cbc77408
> ---[ end trace 266a701a7d4db055 ]---
> Kernel panic - not syncing: Fatal exception
> Dumping ftrace buffer:
>    (ftrace buffer empty)
> Kernel Offset: disabled
> Rebooting in 86400 seconds..
> 
> 
> ---
> This bug is generated by a dumb bot. It may contain errors.
> See https://goo.gl/tpsmEJ for details.
> Direct all questions to syzkaller@xxxxxxxxxxxxxxxxx
> Please credit me with: Reported-by: syzbot <syzkaller@xxxxxxxxxxxxxxxx>
> 
> syzbot will keep track of this bug report.
> Once a fix for this bug is committed, please reply to this email with:
> #syz fix: exact-commit-title

#syz fix: pid: Handle failure to allocate the first pid in a pid namespace