kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] PREEMPT SMP KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 1 PID: 6973 Comm: syz-executor4 Not tainted 4.4.153+ #28
task: ffff8801cf1e0000 task.stack: ffff8800a6d18000
RIP: 0010:[<ffffffff81cc6078>]  [<ffffffff81cc6078>] is_loop_device drivers/block/loop.c:656 [inline]
RIP: 0010:[<ffffffff81cc6078>]  [<ffffffff81cc6078>] loop_validate_file+0x208/0x400 drivers/block/loop.c:667
RSP: 0018:ffff8800a6d1fad0  EFLAGS: 00010206
RAX: 0000000000000036 RBX: dffffc0000000000 RCX: ffffc9000648d000
RDX: 000000000000008d RSI: ffffffff81cc6048 RDI: 00000000000001b0
RBP: ffff8800a6d1fae8 R08: ffff8801cf1e08c8 R09: 0000000000000001
R10: 0000000000000000 R11: 0000000000000001 R12: 0000000000000000
R13: ffff8800b2429cc0 R14: ffff8800b2429cc0 R15: ffff8800ba3960d8
FS:  0000000000000000(0000) GS:ffff8801db700000(0063) knlGS:00000000f570ab40
CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 0000000000606ed8 CR3: 00000000b9821000 CR4: 00000000001606b0
Stack:
 ffff8800ba395f80 ffff8801ce7c8e00 0000000000000004 ffff8800a6d1fb78
 ffffffff81ccf59d ffff8800a68ca008 ffffffff00000001 ffff8800b0456000
 ffff8800b0455400 ffff8800ba395f98 ffff8800a6d1fb70 9ad04945260e7e41
Call Trace:
 [<ffffffff81ccf59d>] loop_change_fd drivers/block/loop.c:713 [inline]
 [<ffffffff81ccf59d>] lo_ioctl+0x3ed/0x16b0 drivers/block/loop.c:1370
 [<ffffffff81cd0912>] lo_compat_ioctl+0xb2/0x140 drivers/block/loop.c:1560
 [<ffffffff81a3edb4>] compat_blkdev_ioctl+0x3a4/0x37eb block/compat_ioctl.c:751
 [<ffffffff8156c10e>] C_SYSC_ioctl fs/compat_ioctl.c:1592 [inline]
 [<ffffffff8156c10e>] compat_SyS_ioctl+0x62e/0x22a0 fs/compat_ioctl.c:1544
 [<ffffffff81005ffe>] do_syscall_32_irqs_on arch/x86/entry/common.c:393 [inline]
 [<ffffffff81005ffe>] do_fast_syscall_32+0x31e/0x8b0 arch/x86/entry/common.c:460
 [<ffffffff8267e410>] sysenter_flags_fixed+0xd/0x1a
Code: 00 00 00 48 89 f8 48 c1 e8 03 80 3c 18 00 0f 85 f7 01 00 00 4d 8b a4 24 f0 00 00 00 49 8d bc 24 b0 01 00 00 48 89 f8 48 c1 e8 03 <80> 3c 18 00 0f 85 cc 01 00 00 4d 8b a4 24 b0 01 00 00 4c 89 e0 
RIP  [<ffffffff81cc6078>] is_loop_device drivers/block/loop.c:656 [inline]
RIP  [<ffffffff81cc6078>] loop_validate_file+0x208/0x400 drivers/block/loop.c:667
 RSP <ffff8800a6d1fad0>
---[ end trace 77de13f1446b9563 ]---