KASAN: null-ptr-deref Write in kcm_tx_work

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 2019fc96 Merge git://git.kernel.org/pub/scm/linux/kernel/g..
git tree: net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=159f2701e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=735296e4dd620b10
dashboard link: https://syzkaller.appspot.com/bug?extid=867331f5ea7690d840b4
compiler: gcc (GCC) 9.0.0 20181231 (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+867331...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: null-ptr-deref in clear_bit include/asm-generic/bitops/instrumented-atomic.h:41 [inline]
BUG: KASAN: null-ptr-deref in kcm_tx_work+0x10e/0x170 net/kcm/kcmsock.c:743
Write of size 8 at addr 0000000000000008 by task kworker/u4:4/280

CPU: 0 PID: 280 Comm: kworker/u4:4 Not tainted 5.6.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: kkcmd kcm_tx_work
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x197/0x210 lib/dump_stack.c:118
__kasan_report.cold+0x5/0x32 mm/kasan/report.c:510
kasan_report+0x12/0x20 mm/kasan/common.c:641
check_memory_region_inline mm/kasan/generic.c:185 [inline]
check_memory_region+0x134/0x1a0 mm/kasan/generic.c:192
__kasan_check_write+0x14/0x20 mm/kasan/common.c:101
clear_bit include/asm-generic/bitops/instrumented-atomic.h:41 [inline]
kcm_tx_work+0x10e/0x170 net/kcm/kcmsock.c:743
process_one_work+0xa05/0x17a0 kernel/workqueue.c:2264
worker_thread+0x98/0xe40 kernel/workqueue.c:2410
kthread+0x361/0x430 kernel/kthread.c:255
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
==================================================================
Kernel panic - not syncing: panic_on_warn set ...
CPU: 0 PID: 280 Comm: kworker/u4:4 Tainted: G B 5.6.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: kkcmd kcm_tx_work
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x197/0x210 lib/dump_stack.c:118
panic+0x2e3/0x75c kernel/panic.c:221
end_report+0x47/0x4f mm/kasan/report.c:96
__kasan_report.cold+0xe/0x32 mm/kasan/report.c:513
kasan_report+0x12/0x20 mm/kasan/common.c:641
check_memory_region_inline mm/kasan/generic.c:185 [inline]
check_memory_region+0x134/0x1a0 mm/kasan/generic.c:192
__kasan_check_write+0x14/0x20 mm/kasan/common.c:101
clear_bit include/asm-generic/bitops/instrumented-atomic.h:41 [inline]
kcm_tx_work+0x10e/0x170 net/kcm/kcmsock.c:743
process_one_work+0xa05/0x17a0 kernel/workqueue.c:2264
worker_thread+0x98/0xe40 kernel/workqueue.c:2410
kthread+0x361/0x430 kernel/kthread.c:255
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
Kernel Offset: disabled
Rebooting in 86400 seconds..


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[syzbot]

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