KASAN: use-after-free Read in rds_queue_reconnect

[syzbot]

Hello,

syzbot hit the following crash on upstream commit
ce380619fab99036f5e745c7a865b21c59f005f6 (Tue Mar 6 04:31:14 2018 +0000)
Merge tag 'please-pull-ia64_misc' of
git://git.kernel.org/pub/scm/linux/kernel/git/aegl/linux

Unfortunately, I don't have any reproducer for this crash yet.
Raw console output is attached.
compiler: gcc (GCC) 7.1.1 20170620
.config is attached.

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Reported-by: syzbot+0c2317...@syzkaller.appspotmail.com
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bond0 (unregistering): Released all slaves
==================================================================
BUG: KASAN: use-after-free in __read_once_size include/linux/compiler.h:188
[inline]
BUG: KASAN: use-after-free in atomic_read arch/x86/include/asm/atomic.h:27
[inline]
BUG: KASAN: use-after-free in refcount_read include/linux/refcount.h:42
[inline]
BUG: KASAN: use-after-free in check_net include/net/net_namespace.h:228
[inline]
BUG: KASAN: use-after-free in rds_destroy_pending net/rds/rds.h:868 [inline]
BUG: KASAN: use-after-free in rds_queue_reconnect+0x89f/0x970
net/rds/threads.c:152
Read of size 4 at addr ffff8801afc6e144 by task kworker/u4:1/21

CPU: 0 PID: 21 Comm: kworker/u4:1 Not tainted 4.16.0-rc4+ #343
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Workqueue: krdsd rds_connect_worker
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_load4_noabort+0x14/0x20 mm/kasan/report.c:432
__read_once_size include/linux/compiler.h:188 [inline]
atomic_read arch/x86/include/asm/atomic.h:27 [inline]
refcount_read include/linux/refcount.h:42 [inline]
check_net include/net/net_namespace.h:228 [inline]
rds_destroy_pending net/rds/rds.h:868 [inline]
rds_queue_reconnect+0x89f/0x970 net/rds/threads.c:152
rds_connect_worker+0x1a2/0x1f0 net/rds/threads.c:183
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 4289:
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
kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:489
kmem_cache_alloc+0x12e/0x760 mm/slab.c:3541
kmem_cache_zalloc include/linux/slab.h:691 [inline]
net_alloc net/core/net_namespace.c:369 [inline]
copy_net_ns+0x152/0x580 net/core/net_namespace.c:409
create_new_namespaces+0x425/0x880 kernel/nsproxy.c:107
unshare_nsproxy_namespaces+0xae/0x1e0 kernel/nsproxy.c:206
SYSC_unshare kernel/fork.c:2407 [inline]
SyS_unshare+0x653/0xfa0 kernel/fork.c:2357
do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
entry_SYSCALL_64_after_hwframe+0x42/0xb7

Freed by task 21:
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]
kmem_cache_free+0x83/0x2a0 mm/slab.c:3743
net_free+0xca/0x110 net/core/net_namespace.c:385
net_drop_ns.part.11+0x26/0x30 net/core/net_namespace.c:392
net_drop_ns net/core/net_namespace.c:391 [inline]
cleanup_net+0x977/0xcb0 net/core/net_namespace.c:535
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

The buggy address belongs to the object at ffff8801afc6e140
which belongs to the cache net_namespace of size 6720
The buggy address is located 4 bytes inside of
6720-byte region [ffff8801afc6e140, ffff8801afc6fb80)
The buggy address belongs to the page:
page:ffffea0006bf1b80 count:1 mapcount:0 mapping:ffff8801afc6e140 index:0x0
compound_mapcount: 0
flags: 0x2fffc0000008100(slab|head)
raw: 02fffc0000008100 ffff8801afc6e140 0000000000000000 0000000100000001
raw: ffffea00072ba120 ffffea0006ec61a0 ffff8801d9bece00 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8801afc6e000: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8801afc6e080: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ffff8801afc6e100: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
^
ffff8801afc6e180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8801afc6e200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
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[Sowmini Varadhan]

#syz dup: KASAN: use-after-free Read in rds_cong_queue_updates