KASAN: use-after-free Read in locks_remove_flock

From: syzbot
Date: Wed Nov 07 2018 - 00:03:08 EST

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Hello,

syzbot found the following crash on:

HEAD commit: d881de30d29e Add linux-next specific files for 20181107
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=16e42f5b400000
kernel config: https://syzkaller.appspot.com/x/.config?x=caa433e1c8778437
dashboard link: https://syzkaller.appspot.com/bug?extid=34a98afb89842107f03f
compiler: gcc (GCC) 8.0.1 20180413 (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+34a98afb89842107f03f@xxxxxxxxxxxxxxxxxxxxxxxxx

==================================================================
BUG: KASAN: use-after-free in locks_remove_flock+0x33c/0x350 fs/locks.c:2567
Read of size 8 at addr ffff8801c92fc040 by task syz-executor1/15515

CPU: 1 PID: 15515 Comm: syz-executor1 Not tainted 4.20.0-rc1-next-20181107+ #107
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x244/0x39d lib/dump_stack.c:113
print_address_description.cold.7+0x9/0x1ff mm/kasan/report.c:256
kasan_report_error mm/kasan/report.c:354 [inline]
kasan_report.cold.8+0x242/0x309 mm/kasan/report.c:412
__asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
locks_remove_flock+0x33c/0x350 fs/locks.c:2567
locks_remove_file+0x148/0x5c0 fs/locks.c:2607
__fput+0x2f0/0xa70 fs/file_table.c:271
____fput+0x15/0x20 fs/file_table.c:312
task_work_run+0x1e8/0x2a0 kernel/task_work.c:113
tracehook_notify_resume include/linux/tracehook.h:188 [inline]
exit_to_usermode_loop+0x318/0x380 arch/x86/entry/common.c:166
prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
do_syscall_64+0x6be/0x820 arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x457569
Code: fd b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 cb b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fc1e8ed4c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000049
RAX: 0000000000000000 RBX: 0000000000000002 RCX: 0000000000457569
RDX: 0000000000000000 RSI: 0000000000000002 RDI: 0000000000000003
RBP: 000000000072bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fc1e8ed56d4
R13: 00000000004bdd9e R14: 00000000004ccdb8 R15: 00000000ffffffff

Allocated by task 15515:
save_stack+0x43/0xd0 mm/kasan/kasan.c:448
set_track mm/kasan/kasan.c:460 [inline]
kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:553
kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:490
kmem_cache_alloc+0x12e/0x730 mm/slab.c:3554
kmem_cache_zalloc include/linux/slab.h:731 [inline]
locks_alloc_lock+0x9e/0x300 fs/locks.c:304
flock_make_lock+0x22c/0x2a0 fs/locks.c:438
__do_sys_flock fs/locks.c:2057 [inline]
__se_sys_flock fs/locks.c:2038 [inline]
__x64_sys_flock+0x12b/0x350 fs/locks.c:2038
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 15515:
save_stack+0x43/0xd0 mm/kasan/kasan.c:448
set_track mm/kasan/kasan.c:460 [inline]
__kasan_slab_free+0x102/0x150 mm/kasan/kasan.c:521
kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
__cache_free mm/slab.c:3498 [inline]
kmem_cache_free+0x83/0x290 mm/slab.c:3760
locks_free_lock+0x295/0x420 fs/locks.c:341
__do_sys_flock fs/locks.c:2078 [inline]
__se_sys_flock fs/locks.c:2038 [inline]
__x64_sys_flock+0x289/0x350 fs/locks.c:2038
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8801c92fc000
which belongs to the cache file_lock_cache of size 264
The buggy address is located 64 bytes inside of
264-byte region [ffff8801c92fc000, ffff8801c92fc108)
The buggy address belongs to the page:
page:ffffea000724bf00 count:1 mapcount:0 mapping:ffff8801d9a1c3c0 index:0x0
flags: 0x2fffc0000000200(slab)
raw: 02fffc0000000200 ffff8801d9a82e48 ffffea00075e1608 ffff8801d9a1c3c0
raw: 0000000000000000 ffff8801c92fc000 000000010000000c 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8801c92fbf00: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
ffff8801c92fbf80: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc

ffff8801c92fc000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

^
ffff8801c92fc080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8801c92fc100: fb fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb
==================================================================
------------[ cut here ]------------
downgrading a read lock
WARNING: CPU: 0 PID: 15521 at kernel/locking/lockdep.c:3556 __lock_downgrade kernel/locking/lockdep.c:3556 [inline]
WARNING: CPU: 0 PID: 15521 at kernel/locking/lockdep.c:3556 lock_downgrade+0x4d7/0x900 kernel/locking/lockdep.c:3819

---
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