KASAN: use-after-free Read in fib_notifier_ops_unregister

[syzbot]

Hello,

syzbot hit the following crash on net-next commit
06b19fe9a6df7aaa423cd8404ebe5ac9ec4b2960 (Sun Apr 1 03:37:33 2018 +0000)
Merge branch 'chelsio-inline-tls'
syzbot dashboard link:
https://syzkaller.appspot.com/bug?extid=70abf378cd8b4682c4c9

Unfortunately, I don't have any reproducer for this crash yet.
Raw console output:
https://syzkaller.appspot.com/x/log.txt?id=6238739898564608
Kernel config:
https://syzkaller.appspot.com/x/.config?id=3327544840960562528
compiler: gcc (GCC) 7.1.1 20170620
CC: [da...@davemloft.net d...@cumulusnetworks.com ido...@mellanox.com
ji...@mellanox.com ktk...@virtuozzo.com linux-...@vger.kernel.org
net...@vger.kernel.org v...@virtuozzo.com]

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Reported-by: syzbot+70abf3...@syzkaller.appspotmail.com
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==================================================================
BUG: KASAN: use-after-free in __list_del_entry_valid+0x10b/0x150
lib/list_debug.c:51
Read of size 8 at addr ffff88019e990908 by task kworker/u4:6/12960

CPU: 1 PID: 12960 Comm: kworker/u4:6 Not tainted 4.16.0-rc6+ #290
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Workqueue: netns cleanup_net
Call Trace:
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0x194/0x24d lib/dump_stack.c:53
print_address_description+0x73/0x250 mm/kasan/report.c:256
kasan_report_error mm/kasan/report.c:354 [inline]
kasan_report+0x23c/0x360 mm/kasan/report.c:412
__asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
__list_del_entry_valid+0x10b/0x150 lib/list_debug.c:51
__list_del_entry include/linux/list.h:117 [inline]
list_del_rcu include/linux/rculist.h:130 [inline]
fib_notifier_ops_unregister+0x6d/0x250 net/core/fib_notifier.c:163
fib6_notifier_exit+0x37/0x50 net/ipv6/fib6_notifier.c:62
fib6_net_exit+0x3c4/0x550 net/ipv6/ip6_fib.c:2166
ops_exit_list.isra.6+0xae/0x150 net/core/net_namespace.c:152
cleanup_net+0x4d8/0xa90 net/core/net_namespace.c:523
process_one_work+0xc47/0x1bb0 kernel/workqueue.c:2113
worker_thread+0x223/0x1990 kernel/workqueue.c:2247
kthread+0x33c/0x400 kernel/kthread.c:238
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:406

Allocated by task 5959:
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:552
__do_kmalloc mm/slab.c:3705 [inline]
__kmalloc+0x162/0x760 mm/slab.c:3714
kmalloc include/linux/slab.h:517 [inline]
kzalloc include/linux/slab.h:701 [inline]
ext4_htree_store_dirent+0x8b/0x580 fs/ext4/dir.c:452
htree_dirblock_to_tree+0x4e8/0xa00 fs/ext4/namei.c:1020
ext4_htree_fill_tree+0x2bb/0xcb0 fs/ext4/namei.c:1097
ext4_dx_readdir fs/ext4/dir.c:576 [inline]
ext4_readdir+0x206a/0x3600 fs/ext4/dir.c:123
iterate_dir+0x1ca/0x530 fs/readdir.c:51
SYSC_getdents fs/readdir.c:231 [inline]
SyS_getdents+0x225/0x450 fs/readdir.c:212
do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
entry_SYSCALL_64_after_hwframe+0x42/0xb7

Freed by task 5959:
save_stack+0x43/0xd0 mm/kasan/kasan.c:447
set_track mm/kasan/kasan.c:459 [inline]
__kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:520
kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:527
__cache_free mm/slab.c:3485 [inline]
kfree+0xd9/0x260 mm/slab.c:3800
free_rb_tree_fname+0x85/0xe0 fs/ext4/dir.c:404
ext4_htree_free_dir_info fs/ext4/dir.c:426 [inline]
ext4_release_dir+0x44/0x60 fs/ext4/dir.c:624
__fput+0x327/0x7e0 fs/file_table.c:209
____fput+0x15/0x20 fs/file_table.c:243
task_work_run+0x199/0x270 kernel/task_work.c:113
tracehook_notify_resume include/linux/tracehook.h:191 [inline]
exit_to_usermode_loop+0x275/0x2f0 arch/x86/entry/common.c:166
prepare_exit_to_usermode arch/x86/entry/common.c:196 [inline]
syscall_return_slowpath arch/x86/entry/common.c:265 [inline]
do_syscall_64+0x6ec/0x940 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x42/0xb7

The buggy address belongs to the object at ffff88019e990900
which belongs to the cache kmalloc-64 of size 64
The buggy address is located 8 bytes inside of
64-byte region [ffff88019e990900, ffff88019e990940)
The buggy address belongs to the page:
page:ffffea00067a6400 count:1 mapcount:0 mapping:ffff88019e990000 index:0x0
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffff88019e990000 0000000000000000 0000000100000020
raw: ffffea00075e6be0 ffffea00067733a0 ffff8801dac00340 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff88019e990800: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
ffff88019e990880: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
> ffff88019e990900: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
^
ffff88019e990980: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
ffff88019e990a00: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
==================================================================


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.