KASAN: null-ptr-deref Write in kthread_use_mm

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    4e78c578 Add linux-next specific files for 20201030
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=148969d4500000
kernel config:  https://syzkaller.appspot.com/x/.config?x=83318758268dc331
dashboard link: https://syzkaller.appspot.com/bug?extid=b57abf7ee60829090495
compiler:       gcc (GCC) 10.1.0-syz 20200507
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=17e1346c500000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1388fbca500000

The issue was bisected to:

commit 4d004099a668c41522242aa146a38cc4eb59cb1e
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date:   Fri Oct 2 09:04:21 2020 +0000

    lockdep: Fix lockdep recursion

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1354e614500000
final oops:     https://syzkaller.appspot.com/x/report.txt?x=10d4e614500000
console output: https://syzkaller.appspot.com/x/log.txt?x=1754e614500000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b57abf7ee60829090495@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 4d004099a668 ("lockdep: Fix lockdep recursion")

==================================================================
BUG: KASAN: null-ptr-deref in instrument_atomic_read_write include/linux/instrumented.h:101 [inline]
BUG: KASAN: null-ptr-deref in atomic_inc include/asm-generic/atomic-instrumented.h:240 [inline]
BUG: KASAN: null-ptr-deref in mmgrab include/linux/sched/mm.h:36 [inline]
BUG: KASAN: null-ptr-deref in kthread_use_mm+0x11c/0x2a0 kernel/kthread.c:1257
Write of size 4 at addr 0000000000000060 by task io_uring-sq/26191

CPU: 1 PID: 26191 Comm: io_uring-sq Not tainted 5.10.0-rc1-next-20201030-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x107/0x163 lib/dump_stack.c:118
 __kasan_report mm/kasan/report.c:549 [inline]
 kasan_report.cold+0x5/0x37 mm/kasan/report.c:562
 check_memory_region_inline mm/kasan/generic.c:186 [inline]
 check_memory_region+0x13d/0x180 mm/kasan/generic.c:192
 instrument_atomic_read_write include/linux/instrumented.h:101 [inline]
 atomic_inc include/asm-generic/atomic-instrumented.h:240 [inline]
 mmgrab include/linux/sched/mm.h:36 [inline]
 kthread_use_mm+0x11c/0x2a0 kernel/kthread.c:1257
 __io_sq_thread_acquire_mm fs/io_uring.c:1092 [inline]
 __io_sq_thread_acquire_mm+0x1c4/0x220 fs/io_uring.c:1085
 io_sq_thread_acquire_mm_files.isra.0+0x125/0x180 fs/io_uring.c:1104
 io_init_req fs/io_uring.c:6661 [inline]
 io_submit_sqes+0x89d/0x25f0 fs/io_uring.c:6757
 __io_sq_thread fs/io_uring.c:6904 [inline]
 io_sq_thread+0x462/0x1630 fs/io_uring.c:6971
 kthread+0x3af/0x4a0 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296
==================================================================
Kernel panic - not syncing: panic_on_warn set ...
CPU: 1 PID: 26191 Comm: io_uring-sq Tainted: G    B             5.10.0-rc1-next-20201030-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x107/0x163 lib/dump_stack.c:118
 panic+0x306/0x73d kernel/panic.c:231
 end_report+0x58/0x5e mm/kasan/report.c:106
 __kasan_report mm/kasan/report.c:552 [inline]
 kasan_report.cold+0xd/0x37 mm/kasan/report.c:562
 check_memory_region_inline mm/kasan/generic.c:186 [inline]
 check_memory_region+0x13d/0x180 mm/kasan/generic.c:192
 instrument_atomic_read_write include/linux/instrumented.h:101 [inline]
 atomic_inc include/asm-generic/atomic-instrumented.h:240 [inline]
 mmgrab include/linux/sched/mm.h:36 [inline]
 kthread_use_mm+0x11c/0x2a0 kernel/kthread.c:1257
 __io_sq_thread_acquire_mm fs/io_uring.c:1092 [inline]
 __io_sq_thread_acquire_mm+0x1c4/0x220 fs/io_uring.c:1085
 io_sq_thread_acquire_mm_files.isra.0+0x125/0x180 fs/io_uring.c:1104
 io_init_req fs/io_uring.c:6661 [inline]
 io_submit_sqes+0x89d/0x25f0 fs/io_uring.c:6757
 __io_sq_thread fs/io_uring.c:6904 [inline]
 io_sq_thread+0x462/0x1630 fs/io_uring.c:6971
 kthread+0x3af/0x4a0 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296
Kernel Offset: disabled
Rebooting in 86400 seconds..


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