general protection fault in relay_switch_subbuf

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 9aa0219c6a4c Add linux-next specific files for 20180926
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=17430831400000
kernel config: https://syzkaller.appspot.com/x/.config?x=47acd6bd92246baa
dashboard link: https://syzkaller.appspot.com/bug?extid=7e9bcba1bb0348cf7cd3
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
CC: [ak...@linux-foundation.org ebig...@google.com
jrdr....@gmail.com kees...@chromium.org linux-...@vger.kernel.org
rien...@google.com vi...@zeniv.linux.org.uk]

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+7e9bcb...@syzkaller.appspotmail.com

relay: one or more items not logged [item size (56) > sub-buffer size (5)]
kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 17638 Comm: syz-executor2 Not tainted 4.19.0-rc5-next-20180926+
#81
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
RIP: 0010:relay_switch_subbuf+0x27e/0xa70 kernel/relay.c:753
Code: 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 a4 07 00 00 48 b8 00 00 00 00
00 fc ff df 4c 8b 73 58 49 8d 7e 50 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f
85 8b 07 00 00 48 ba 00 00 00 00 00 fc ff df 4d 8b
RSP: 0018:ffff8801d3297618 EFLAGS: 00010206
RAX: dffffc0000000000 RBX: ffff88017e875340 RCX: ffffc90005ea2000
RDX: 000000000000000a RSI: ffffffff817e0ab6 RDI: 0000000000000050
RBP: ffff8801d32976d8 R08: ffff8801c45fe140 R09: fffffbfff12fa760
R10: ffff8801d32976d8 R11: ffffffff897d3b07 R12: ffff8801c7060000
R13: ffff8801d74ffb80 R14: 0000000000000000 R15: 0000000000000000
FS: 00007f98962e2700(0000) GS:ffff8801dac00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000001b9d7d0 CR3: 00000001d36bf000 CR4: 00000000001406f0
Call Trace:
relay_flush+0x1c6/0x280 kernel/relay.c:881
__blk_trace_startstop.isra.20+0x2ae/0x8c0 kernel/trace/blktrace.c:668
blk_trace_ioctl+0x226/0x2f0 kernel/trace/blktrace.c:727
blkdev_ioctl+0x8bc/0x2010 block/ioctl.c:587
block_ioctl+0xee/0x130 fs/block_dev.c:1883
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:501 [inline]
do_vfs_ioctl+0x1de/0x1720 fs/ioctl.c:685
ksys_ioctl+0xa9/0xd0 fs/ioctl.c:702
__do_sys_ioctl fs/ioctl.c:709 [inline]
__se_sys_ioctl fs/ioctl.c:707 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:707
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x457579
Code: 1d b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff
ff 0f 83 eb b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f98962e1c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000457579
RDX: 0000000000000000 RSI: 0000000000001275 RDI: 0000000000000004
RBP: 000000000072bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f98962e26d4
R13: 00000000004bea0b R14: 00000000004ce710 R15: 00000000ffffffff
Modules linked in:
---[ end trace d1e8a68b60b5b937 ]---
RIP: 0010:relay_switch_subbuf+0x27e/0xa70 kernel/relay.c:753
attempt to access beyond end of device
loop5: rw=1, want=130, limit=112
Code: 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 a4 07 00 00 48 b8 00 00 00 00
00 fc ff df 4c 8b 73 58 49 8d 7e 50 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f
85 8b 07 00 00 48 ba 00 00 00 00 00 fc ff df 4d 8b
Buffer I/O error on dev loop5, logical block 129, lost async page write
RSP: 0018:ffff8801d3297618 EFLAGS: 00010206
kobject: 'loop1' (00000000466bacae): kobject_uevent_env
RAX: dffffc0000000000 RBX: ffff88017e875340 RCX: ffffc90005ea2000
RDX: 000000000000000a RSI: ffffffff817e0ab6 RDI: 0000000000000050
kobject: 'loop1' (00000000466bacae): fill_kobj_path: path
= '/devices/virtual/block/loop1'
attempt to access beyond end of device
RBP: ffff8801d32976d8 R08: ffff8801c45fe140 R09: fffffbfff12fa760
loop5: rw=1, want=131, limit=112
R10: ffff8801d32976d8 R11: ffffffff897d3b07 R12: ffff8801c7060000
R13: ffff8801d74ffb80 R14: 0000000000000000 R15: 0000000000000000
Buffer I/O error on dev loop5, logical block 130, lost async page write
FS: 00007f98962e2700(0000) GS:ffff8801dad00000(0000) knlGS:0000000000000000
attempt to access beyond end of device
kobject: 'loop0' (00000000d43bbfb5): kobject_uevent_env
loop5: rw=1, want=132, limit=112
kobject: 'loop0' (00000000d43bbfb5): fill_kobj_path: path
= '/devices/virtual/block/loop0'
Buffer I/O error on dev loop5, logical block 131, lost async page write
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
attempt to access beyond end of device
CR2: 00007f0be6af1000 CR3: 00000001d36bf000 CR4: 00000000001406e0


---
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[Dmitry Vyukov]

#syz upstream

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