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SubjectKASAN: use-after-free Read in brnf_exit_net
From
Hello,

syzbot found the following crash on:

HEAD commit: 1c6b4050 Add linux-next specific files for 20190618
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=10126209a00000
kernel config: https://syzkaller.appspot.com/x/.config?x=3c614278993de456
dashboard link: https://syzkaller.appspot.com/bug?extid=43a3fa52c0d9c5c94f41
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16291176a00000

The bug was bisected to:

commit b38d37a08ec4b19a9b9ec3a1ff5566781fcae1f1
Author: Stephen Rothwell <sfr@canb.auug.org.au>
Date: Tue Jun 18 04:19:55 2019 +0000

Merge remote-tracking branch 'drm/drm-next'

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=146f914ea00000
final crash: https://syzkaller.appspot.com/x/report.txt?x=166f914ea00000
console output: https://syzkaller.appspot.com/x/log.txt?x=126f914ea00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+43a3fa52c0d9c5c94f41@syzkaller.appspotmail.com
Fixes: b38d37a08ec4 ("Merge remote-tracking branch 'drm/drm-next'")

==================================================================
BUG: KASAN: use-after-free in br_netfilter_sysctl_exit_net
net/bridge/br_netfilter_hooks.c:1121 [inline]
BUG: KASAN: use-after-free in brnf_exit_net+0x38c/0x3a0
net/bridge/br_netfilter_hooks.c:1141
Read of size 8 at addr ffff8880a4078d60 by task kworker/u4:4/8749

CPU: 0 PID: 8749 Comm: kworker/u4:4 Not tainted 5.2.0-rc5-next-20190618 #17
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:77 [inline]
dump_stack+0x172/0x1f0 lib/dump_stack.c:113
print_address_description.cold+0xd4/0x306 mm/kasan/report.c:351
__kasan_report.cold+0x1b/0x36 mm/kasan/report.c:482
kasan_report+0x12/0x20 mm/kasan/common.c:614
__asan_report_load8_noabort+0x14/0x20 mm/kasan/generic_report.c:132
br_netfilter_sysctl_exit_net net/bridge/br_netfilter_hooks.c:1121 [inline]
brnf_exit_net+0x38c/0x3a0 net/bridge/br_netfilter_hooks.c:1141
ops_exit_list.isra.0+0xaa/0x150 net/core/net_namespace.c:154
cleanup_net+0x3fb/0x960 net/core/net_namespace.c:553
process_one_work+0x989/0x1790 kernel/workqueue.c:2269
worker_thread+0x98/0xe40 kernel/workqueue.c:2415
kthread+0x354/0x420 kernel/kthread.c:255
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

Allocated by task 11374:
save_stack+0x23/0x90 mm/kasan/common.c:71
set_track mm/kasan/common.c:79 [inline]
__kasan_kmalloc mm/kasan/common.c:489 [inline]
__kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:462
kasan_kmalloc+0x9/0x10 mm/kasan/common.c:503
__do_kmalloc mm/slab.c:3645 [inline]
__kmalloc+0x15c/0x740 mm/slab.c:3654
kmalloc include/linux/slab.h:552 [inline]
kzalloc include/linux/slab.h:743 [inline]
__register_sysctl_table+0xc7/0xef0 fs/proc/proc_sysctl.c:1327
register_net_sysctl+0x29/0x30 net/sysctl_net.c:121
br_netfilter_sysctl_init_net net/bridge/br_netfilter_hooks.c:1105 [inline]
brnf_init_net+0x379/0x6a0 net/bridge/br_netfilter_hooks.c:1126
ops_init+0xb3/0x410 net/core/net_namespace.c:130
setup_net+0x2d3/0x740 net/core/net_namespace.c:316
copy_net_ns+0x1df/0x340 net/core/net_namespace.c:439
create_new_namespaces+0x400/0x7b0 kernel/nsproxy.c:103
unshare_nsproxy_namespaces+0xc2/0x200 kernel/nsproxy.c:202
ksys_unshare+0x444/0x980 kernel/fork.c:2822
__do_sys_unshare kernel/fork.c:2890 [inline]
__se_sys_unshare kernel/fork.c:2888 [inline]
__x64_sys_unshare+0x31/0x40 kernel/fork.c:2888
do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 9:
save_stack+0x23/0x90 mm/kasan/common.c:71
set_track mm/kasan/common.c:79 [inline]
__kasan_slab_free+0x102/0x150 mm/kasan/common.c:451
kasan_slab_free+0xe/0x10 mm/kasan/common.c:459
__cache_free mm/slab.c:3417 [inline]
kfree+0x10a/0x2c0 mm/slab.c:3746
__rcu_reclaim kernel/rcu/rcu.h:215 [inline]
rcu_do_batch kernel/rcu/tree.c:2092 [inline]
invoke_rcu_callbacks kernel/rcu/tree.c:2310 [inline]
rcu_core+0xcc7/0x1500 kernel/rcu/tree.c:2291
__do_softirq+0x25c/0x94c kernel/softirq.c:292

The buggy address belongs to the object at ffff8880a4078d40
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 32 bytes inside of
512-byte region [ffff8880a4078d40, ffff8880a4078f40)
The buggy address belongs to the page:
page:ffffea0002901e00 refcount:1 mapcount:0 mapping:ffff8880aa400a80
index:0xffff8880a40785c0
flags: 0x1fffc0000000200(slab)
raw: 01fffc0000000200 ffffea0001d636c8 ffffea0001b07308 ffff8880aa400a80
raw: ffff8880a40785c0 ffff8880a40780c0 0000000100000004 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8880a4078c00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8880a4078c80: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
> ffff8880a4078d00: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
^
ffff8880a4078d80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8880a4078e00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
For information about bisection process see: https://goo.gl/tpsmEJ#bisection
syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

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