syzbot

BUG: unable to handle kernel NULL pointer dereference at 00000000000000fc
IP: qlink_to_object mm/kasan/quarantine.c:136 [inline]
IP: qlink_free mm/kasan/quarantine.c:141 [inline]
IP: qlist_free_all+0x28/0x140 mm/kasan/quarantine.c:166
PGD 0 P4D 0 
Oops: 0000 [#1] PREEMPT SMP KASAN
Modules linked in:
CPU: 0 PID: 29945 Comm: kworker/u4:0 Not tainted 4.14.232-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff88804695c400 task.stack: ffff88821d6f0000
RIP: 0010:qlink_to_object mm/kasan/quarantine.c:136 [inline]
RIP: 0010:qlink_free mm/kasan/quarantine.c:141 [inline]
RIP: 0010:qlist_free_all+0x28/0x140 mm/kasan/quarantine.c:166
RSP: 0018:ffff88821d6f7c08 EFLAGS: 00010246
RAX: ffffea0000000000 RBX: ffff888000000000 RCX: ffffea000000001f
RDX: 0000000000000000 RSI: ffff88804695cc88 RDI: ffff888000000000
RBP: 0000000000000000 R08: ffffea00024d6000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff888000000000
R13: ffff88821d6f7c40 R14: 0000000000000000 R15: 0000000000000286
FS:  0000000000000000(0000) GS:ffff8880ba400000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000000000fc CR3: 000000009b7e7000 CR4: 00000000001426f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 quarantine_reduce+0x185/0x200 mm/kasan/quarantine.c:259
 kasan_kmalloc+0xa2/0x160 mm/kasan/kasan.c:536
 slab_post_alloc_hook mm/slab.h:442 [inline]
 slab_alloc mm/slab.c:3390 [inline]
 kmem_cache_alloc+0x111/0x3c0 mm/slab.c:3550
 prepare_kernel_cred+0x21/0x990 kernel/cred.c:625
 call_usermodehelper_exec_async+0x112/0x510 kernel/umh.c:89
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:404
Code: 90 90 90 41 57 41 56 41 55 41 54 55 53 48 8b 1f 48 85 db 0f 84 08 01 00 00 48 89 f5 49 89 fd 48 85 ed 49 89 ee 0f 84 8b 00 00 00 <49> 63 86 fc 00 00 00 4c 8b 23 48 29 c3 48 83 3d 53 c3 71 07 00 
RIP: qlink_to_object mm/kasan/quarantine.c:136 [inline] RSP: ffff88821d6f7c08
RIP: qlink_free mm/kasan/quarantine.c:141 [inline] RSP: ffff88821d6f7c08
RIP: qlist_free_all+0x28/0x140 mm/kasan/quarantine.c:166 RSP: ffff88821d6f7c08
CR2: 00000000000000fc
---[ end trace 863012eaa57ffca4 ]---