general protection fault in lo_ioctl (2)

[syzbot <syzbot+bf89c128e05dd6c62523@syzkaller.appspotmail.com>]

Hello,

syzbot found the following crash on:

HEAD commit:    fff75eb2a08c Merge tag 'errseq-v4.17' of  
git://git.kernel.o...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?id=5301511529693184
kernel config:   
https://syzkaller.appspot.com/x/.config?id=6493557782959164711
dashboard link: https://syzkaller.appspot.com/bug?extid=bf89c128e05dd6c62523
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
userspace arch: i386
syzkaller  
repro:https://syzkaller.appspot.com/x/repro.syz?id=5000693362458624

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+bf89c128e05dd6c62523@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] SMP KASAN
Dumping ftrace buffer:
    (ftrace buffer empty)
Modules linked in:
CPU: 0 PID: 10637 Comm: syz-executor1 Not tainted 4.17.0-rc3+ #52
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
RIP: 0010:loop_set_fd drivers/block/loop.c:901 [inline]
RIP: 0010:lo_ioctl+0x1ae8/0x2130 drivers/block/loop.c:1397
RSP: 0018:ffff8801bd6dfc08 EFLAGS: 00010202
RAX: 0000000000000037 RBX: ffff8801d296db00 RCX: dffffc0000000000
RDX: 0000000000000000 RSI: ffffffff84b2cd57 RDI: 00000000000001b8
RBP: ffff8801bd6dfc80 R08: ffff8801c46943c0 R09: ffffed003b5c46c2
R10: 0000000000000003 R11: 0000000000000001 R12: 0000000000000000
R13: 0000000000000000 R14: ffff8801b58561a0 R15: ffff8801b58560c0
FS:  0000000000000000(0000) GS:ffff8801dae00000(0063) knlGS:00000000f7f2eb40
CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 0000000008138024 CR3: 00000001d03df000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
  lo_compat_ioctl+0xc1/0x170 drivers/block/loop.c:1602
  compat_blkdev_ioctl+0x3c2/0x1b20 block/compat_ioctl.c:406
  __do_compat_sys_ioctl fs/compat_ioctl.c:1461 [inline]
  __se_compat_sys_ioctl fs/compat_ioctl.c:1407 [inline]
  __ia32_compat_sys_ioctl+0x221/0x640 fs/compat_ioctl.c:1407
  do_syscall_32_irqs_on arch/x86/entry/common.c:323 [inline]
  do_fast_syscall_32+0x345/0xf9b arch/x86/entry/common.c:394
  entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139
RIP: 0023:0xf7f32cb9
RSP: 002b:00000000f7f2e0ac EFLAGS: 00000282 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 0000000000000004 RCX: 0000000000004c00
RDX: 0000000000000003 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000292 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
Code: e8 03 80 3c 08 00 0f 85 2c 02 00 00 4d 8b ad f0 00 00 00 48 b9 00 00  
00 00 00 fc ff df 49 8d bd b8 01 00 00 48 89 f8 48 c1 e8 03 <80> 3c 08 00  
0f 85 f9 01 00 00 4d 8b ad b8 01 00 00 48 b9 00 00
RIP: loop_set_fd drivers/block/loop.c:901 [inline] RSP: ffff8801bd6dfc08
RIP: lo_ioctl+0x1ae8/0x2130 drivers/block/loop.c:1397 RSP: ffff8801bd6dfc08
---[ end trace a15583efe355602c ]---


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