KASAN: null-ptr-deref Write in l2cap_chan_put

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 5631c5e0 Merge tag 'xfs-5.9-merge-7' of git://git.kernel.o..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15c21934900000
kernel config: https://syzkaller.appspot.com/x/.config?x=afba7c06f91e56eb
dashboard link: https://syzkaller.appspot.com/bug?extid=452e9465a3b2817fa4c2
compiler: gcc (GCC) 10.1.0-syz 20200507
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=131e96aa900000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+452e94...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: null-ptr-deref in instrument_atomic_write include/linux/instrumented.h:71 [inline]
BUG: KASAN: null-ptr-deref in atomic_fetch_sub_release include/asm-generic/atomic-instrumented.h:220 [inline]
BUG: KASAN: null-ptr-deref in refcount_sub_and_test include/linux/refcount.h:266 [inline]
BUG: KASAN: null-ptr-deref in refcount_dec_and_test include/linux/refcount.h:294 [inline]
BUG: KASAN: null-ptr-deref in kref_put include/linux/kref.h:64 [inline]
BUG: KASAN: null-ptr-deref in l2cap_chan_put+0x28/0x230 net/bluetooth/l2cap_core.c:502
Write of size 4 at addr 0000000000000018 by task kworker/0:1/7077

CPU: 0 PID: 7077 Comm: kworker/0:1 Not tainted 5.8.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events l2cap_chan_timeout
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x18f/0x20d lib/dump_stack.c:118
__kasan_report mm/kasan/report.c:517 [inline]
kasan_report.cold+0x5/0x37 mm/kasan/report.c:530
check_memory_region_inline mm/kasan/generic.c:186 [inline]
check_memory_region+0x13d/0x180 mm/kasan/generic.c:192
instrument_atomic_write include/linux/instrumented.h:71 [inline]
atomic_fetch_sub_release include/asm-generic/atomic-instrumented.h:220 [inline]
refcount_sub_and_test include/linux/refcount.h:266 [inline]
refcount_dec_and_test include/linux/refcount.h:294 [inline]
kref_put include/linux/kref.h:64 [inline]
l2cap_chan_put+0x28/0x230 net/bluetooth/l2cap_core.c:502
l2cap_sock_kill+0xbd/0x180 net/bluetooth/l2cap_sock.c:1217
l2cap_chan_timeout+0x1c1/0x450 net/bluetooth/l2cap_core.c:438
process_one_work+0x94c/0x1670 kernel/workqueue.c:2269
worker_thread+0x64c/0x1120 kernel/workqueue.c:2415
kthread+0x3b5/0x4a0 kernel/kthread.c:292
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
==================================================================
Kernel panic - not syncing: panic_on_warn set ...
CPU: 0 PID: 7077 Comm: kworker/0:1 Tainted: G B 5.8.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events l2cap_chan_timeout
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x18f/0x20d lib/dump_stack.c:118
panic+0x2e3/0x75c kernel/panic.c:231
end_report+0x4d/0x53 mm/kasan/report.c:104
__kasan_report mm/kasan/report.c:520 [inline]
kasan_report.cold+0xd/0x37 mm/kasan/report.c:530
check_memory_region_inline mm/kasan/generic.c:186 [inline]
check_memory_region+0x13d/0x180 mm/kasan/generic.c:192
instrument_atomic_write include/linux/instrumented.h:71 [inline]
atomic_fetch_sub_release include/asm-generic/atomic-instrumented.h:220 [inline]
refcount_sub_and_test include/linux/refcount.h:266 [inline]
refcount_dec_and_test include/linux/refcount.h:294 [inline]
kref_put include/linux/kref.h:64 [inline]
l2cap_chan_put+0x28/0x230 net/bluetooth/l2cap_core.c:502
l2cap_sock_kill+0xbd/0x180 net/bluetooth/l2cap_sock.c:1217
l2cap_chan_timeout+0x1c1/0x450 net/bluetooth/l2cap_core.c:438
process_one_work+0x94c/0x1670 kernel/workqueue.c:2269
worker_thread+0x64c/0x1120 kernel/workqueue.c:2415
kthread+0x3b5/0x4a0 kernel/kthread.c:292
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
Kernel Offset: disabled
Rebooting in 86400 seconds..


---
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[syzbot]

syzbot suspects this issue was fixed by commit:

commit 1bff51ea59a9afb67d2dd78518ab0582a54a472c
Author: Wang ShaoBo <bobo.sh...@huawei.com>
Date: Wed Sep 1 00:35:37 2021 +0000

Bluetooth: fix use-after-free error in lock_sock_nested()

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=141cfa45b00000
start commit: c70672d8d316 Merge tag 's390-5.9-5' of git://git.kernel.or..
git tree: upstream
kernel config: https://syzkaller.appspot.com/x/.config?x=bd46548257448703
dashboard link: https://syzkaller.appspot.com/bug?extid=452e9465a3b2817fa4c2
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=152f31f9900000

If the result looks correct, please mark the issue as fixed by replying with:

#syz fix: Bluetooth: fix use-after-free error in lock_sock_nested()

For information about bisection process see: https://goo.gl/tpsmEJ#bisection

[Dmitry Vyukov]

Looks reasonable: