audit: type=1400 audit(1513628045.860:7): avc:  denied  { map } for  pid=3143 comm="syzkaller987613" path="/root/syzkaller987613502" dev="sda1" ino=16481 scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tcontext=unconfined_u:object_r:user_home_t:s0 tclass=file permissive=1
==================================================================
BUG: KASAN: use-after-free in handle_userfault+0x21c1/0x24c0 fs/userfaultfd.c:371
Read of size 8 at addr ffff8801c8c86da0 by task syzkaller987613/3150

CPU: 0 PID: 3150 Comm: syzkaller987613 Not tainted 4.15.0-rc4+ #137
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x194/0x257 lib/dump_stack.c:53
 print_address_description+0x73/0x250 mm/kasan/report.c:252
 kasan_report_error mm/kasan/report.c:351 [inline]
 kasan_report+0x25b/0x340 mm/kasan/report.c:409
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:430
 handle_userfault+0x21c1/0x24c0 fs/userfaultfd.c:371
 do_huge_pmd_anonymous_page+0xe2c/0x1b00 mm/huge_memory.c:707
 create_huge_pmd mm/memory.c:3828 [inline]
 __handle_mm_fault+0x1a0c/0x3ce0 mm/memory.c:4032
 handle_mm_fault+0x334/0x8d0 mm/memory.c:4098
 __do_page_fault+0x5c9/0xc90 arch/x86/mm/fault.c:1429
 do_page_fault+0xee/0x720 arch/x86/mm/fault.c:1504
 page_fault+0x22/0x30 arch/x86/entry/entry_64.S:1094
RIP: 0023:0xf7fc3c79
RSP: 002b:0000000020687000 EFLAGS: 00010296
RAX: 0000000000000000 RBX: 0000000000000600 RCX: 0000000020687000
RDX: 0000000020b4c000 RSI: 0000000020552ffc RDI: 00000000207a4f71
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 3148:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:551
 kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:489
 kmem_cache_alloc+0x12e/0x760 mm/slab.c:3544
 dup_userfaultfd+0x21c/0x890 fs/userfaultfd.c:659
 dup_mmap kernel/fork.c:662 [inline]
 dup_mm kernel/fork.c:1197 [inline]
 copy_mm+0xa38/0x1310 kernel/fork.c:1251
 copy_process.part.38+0x1eb9/0x4ac0 kernel/fork.c:1753
 copy_process kernel/fork.c:1566 [inline]
 _do_fork+0x1ef/0xfb0 kernel/fork.c:2045
 SYSC_clone kernel/fork.c:2155 [inline]
 SyS_clone+0x37/0x50 kernel/fork.c:2149
 do_syscall_32_irqs_on arch/x86/entry/common.c:327 [inline]
 do_fast_syscall_32+0x3ee/0xf9d arch/x86/entry/common.c:389
 entry_SYSENTER_compat+0x51/0x60 arch/x86/entry/entry_64_compat.S:125

Freed by task 3148:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_slab_free+0x71/0xc0 mm/kasan/kasan.c:524
 __cache_free mm/slab.c:3488 [inline]
 kmem_cache_free+0x77/0x280 mm/slab.c:3746
 userfaultfd_ctx_put+0x50c/0x740 fs/userfaultfd.c:165
 userfaultfd_event_wait_completion+0x86d/0xae0 fs/userfaultfd.c:605
 dup_fctx fs/userfaultfd.c:693 [inline]
 dup_userfaultfd_complete+0x2de/0x480 fs/userfaultfd.c:701
 dup_mmap kernel/fork.c:730 [inline]
 dup_mm kernel/fork.c:1197 [inline]
 copy_mm+0xe9b/0x1310 kernel/fork.c:1251
 copy_process.part.38+0x1eb9/0x4ac0 kernel/fork.c:1753
 copy_process kernel/fork.c:1566 [inline]
 _do_fork+0x1ef/0xfb0 kernel/fork.c:2045
 SYSC_clone kernel/fork.c:2155 [inline]
 SyS_clone+0x37/0x50 kernel/fork.c:2149
 do_syscall_32_irqs_on arch/x86/entry/common.c:327 [inline]
 do_fast_syscall_32+0x3ee/0xf9d arch/x86/entry/common.c:389
 entry_SYSENTER_compat+0x51/0x60 arch/x86/entry/entry_64_compat.S:125

The buggy address belongs to the object at ffff8801c8c86c40
 which belongs to the cache userfaultfd_ctx_cache of size 360
The buggy address is located 352 bytes inside of
 360-byte region [ffff8801c8c86c40, ffff8801c8c86da8)
The buggy address belongs to the page:
page:00000000d5bd414a count:1 mapcount:0 mapping:000000003fa120bd index:0xffff8801c8c86ff7
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffff8801c8c86000 ffff8801c8c86ff7 0000000100000009
raw: ffff8801d6b35f48 ffff8801d6b35f48 ffff8801d6805000 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801c8c86c80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801c8c86d00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8801c8c86d80: fb fb fb fb fb fc fc fc fc fc fc fc fc fc fc fc
                               ^
 ffff8801c8c86e00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801c8c86e80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================