Re: BUG: unable to handle kernel paging request in memset_erms (2)

[Eric Biggers]

On Fri, Jan 19, 2018 at 01:58:01PM -0800, syzbot wrote:
> Hello,
> 
> syzbot hit the following crash on mmots commit
> 2164355612187e55e8d60a28d2cc6b2337841a7e (Fri Jan 19 01:07:54 2018 +0000)
> pci: test for unexpectedly disabled bridges
> 
> So far this crash happened 2 times on mmots.
> C reproducer is attached.
> syzkaller reproducer is attached.
> Raw console output is attached.
> compiler: gcc (GCC) 7.1.1 20170620
> .config is attached.
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+29f08ad5cb6820798dfe@xxxxxxxxxxxxxxxxxxxxxxxxx
> It will help syzbot understand when the bug is fixed. See footer for
> details.
> If you forward the report, please keep this part and the footer.
> 
> BUG: unable to handle kernel paging request at ffffc90001691000
> IP: memset_erms+0x9/0x10 arch/x86/lib/memset_64.S:65
> PGD 1dad2c067 P4D 1dad2c067 PUD 1dad2d067 PMD 1c6a8f067 PTE 0
> Oops: 0002 [#1] SMP KASAN
> Dumping ftrace buffer:
>    (ftrace buffer empty)
> Modules linked in:
> CPU: 1 PID: 5739 Comm: syzkaller592073 Not tainted 4.15.0-rc8-mm1+ #57
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> RIP: 0010:memset_erms+0x9/0x10 arch/x86/lib/memset_64.S:65
> RSP: 0018:ffff8801cbbdfb78 EFLAGS: 00010246
> RAX: fffff520002d3f00 RBX: ffffc90001691000 RCX: 000000000000ee51
> RDX: 000000000000ee51 RSI: 0000000000000000 RDI: ffffc90001691000
> RBP: ffff8801cbbdfb98 R08: fffff520002d3fcb R09: ffffc90001691000
> R10: 0000000000001dcb R11: fffff520002d3fca R12: 000000000000ee51
> R13: 0000000000000000 R14: 00007ffffffff000 R15: 000000002001be51
> FS:  00007f88ae7d7700(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: ffffc90001691000 CR3: 00000001ccefa005 CR4: 00000000001606e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  memset include/linux/string.h:329 [inline]
>  _copy_from_user+0xe9/0x110 lib/usercopy.c:16
>  copy_from_user include/linux/uaccess.h:147 [inline]
>  snd_pcm_oss_write1 sound/core/oss/pcm_oss.c:1347 [inline]
>  snd_pcm_oss_write+0x438/0x880 sound/core/oss/pcm_oss.c:2659
>  __vfs_write+0xef/0x970 fs/read_write.c:480
>  vfs_write+0x189/0x510 fs/read_write.c:544
>  SYSC_write fs/read_write.c:589 [inline]
>  SyS_write+0xef/0x220 fs/read_write.c:581
>  entry_SYSCALL_64_fastpath+0x29/0xa0
> RIP: 0033:0x44a559
> RSP: 002b:00007f88ae7d6da8 EFLAGS: 00000293 ORIG_RAX: 0000000000000001
> RAX: ffffffffffffffda RBX: 00000000006dcc24 RCX: 000000000044a559
> RDX: 000000000000fe51 RSI: 000000002000c000 RDI: 0000000000000003
> RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000293 R12: 00000000006dcc20
> R13: 7073642f7665642f R14: 00800000c0045006 R15: 0000000000000001
> Code: 48 c1 e9 03 40 0f b6 f6 48 b8 01 01 01 01 01 01 01 01 48 0f af c6 f3
> 48 ab 89 d1 f3 aa 4c 89 c8 c3 90 49 89 f9 40 88 f0 48 89 d1 <f3> aa 4c 89 c8
> c3 90 49 89 fa 40 0f b6 ce 48 b8 01 01 01 01 01
> RIP: memset_erms+0x9/0x10 arch/x86/lib/memset_64.S:65 RSP: ffff8801cbbdfb78
> CR2: ffffc90001691000
> ---[ end trace 8f421641f3e10f44 ]---
> 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.
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> 
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> #syz fix: exact-commit-title

The reproducer is unreliable, but this is another one that seems to have been
fixed by commit 02a5d6925cd34:

#syz fix: ALSA: pcm: Avoid potential races between OSS ioctls and read/write

The reproducer is opening /dev/dsp1, then concurrently doing write() and
ioctl(SNDCTL_DSP_CHANNELS).

- Eric