general protection fault in relay_open_buf

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 78d697fc Linux 4.14.172
git tree: linux-4.14.y
console output: https://syzkaller.appspot.com/x/log.txt?x=10d93d31e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=31ad682bcda9b93f
dashboard link: https://syzkaller.appspot.com/bug?extid=2a72de2b98eb04ecd9c9
compiler: gcc (GCC) 9.0.0 20181231 (experimental)

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+2a72de...@syzkaller.appspotmail.com

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
Modules linked in:
CPU: 0 PID: 15367 Comm: syz-executor.2 Not tainted 4.14.172-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8880a402e4c0 task.stack: ffff8880a4af0000
RIP: 0010:relay_set_buf_dentry kernel/relay.c:411 [inline]
RIP: 0010:relay_open_buf.part.0+0x733/0x9d0 kernel/relay.c:459
RSP: 0018:ffff8880a4af7a00 EFLAGS: 00010206
RAX: dffffc0000000000 RBX: ffff888088a735c0 RCX: ffffc90008628000
RDX: 000000000000000a RSI: ffffffff815af705 RDI: 0000000000000050
RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff8880a0edea40
R13: 0000000000000000 R14: 0000000000000100 R15: 0000000000000100
FS: 00007f11da6db700(0000) GS:ffff8880aea00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000748008 CR3: 000000008daec000 CR4: 00000000001426f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
relay_open_buf kernel/relay.c:448 [inline]
relay_open kernel/relay.c:598 [inline]
relay_open+0x4d9/0x910 kernel/relay.c:562
do_blk_trace_setup+0x3b4/0xad0 kernel/trace/blktrace.c:533
blk_trace_setup+0xa3/0x120 kernel/trace/blktrace.c:579
blk_trace_ioctl+0x13b/0x260 kernel/trace/blktrace.c:694
blkdev_ioctl+0xe9/0x17d0 block/ioctl.c:580
block_ioctl+0xd9/0x120 fs/block_dev.c:1881
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:500 [inline]
do_vfs_ioctl+0x75a/0xfe0 fs/ioctl.c:684
SYSC_ioctl fs/ioctl.c:701 [inline]
SyS_ioctl+0x7f/0xb0 fs/ioctl.c:692
do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x45c479
RSP: 002b:00007f11da6dac78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f11da6db6d4 RCX: 000000000045c479
RDX: 0000000020000080 RSI: 00000000c0481273 RDI: 0000000000000006
RBP: 000000000076bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000228 R14: 00000000004c40ee R15: 000000000076bf2c
Code: df 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 9d 02 00 00 48 b8 00 00 00 00 00 fc ff df 48 8b 6d 58 48 8d 7d 50 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 70 02 00 00 4c 89 6d 50 4c 8d 6b 48 e9 25 fe
RIP: relay_set_buf_dentry kernel/relay.c:411 [inline] RSP: ffff8880a4af7a00
RIP: relay_open_buf.part.0+0x733/0x9d0 kernel/relay.c:459 RSP: ffff8880a4af7a00
---[ end trace 8bc41f312099c175 ]---


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.