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Hello,

syzbot found the following crash on:

HEAD commit: 22051d9c Merge tag 'platform-drivers-x86-v5.3-2' of git://..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12dab5a4600000
kernel config: https://syzkaller.appspot.com/x/.config?x=135cb826ac59d7fc
dashboard link: https://syzkaller.appspot.com/bug?extid=7f067c796eee2acbc57a
compiler: clang version 9.0.0 (/home/glider/llvm/clang
80fee25776c2fb61e74c1ecb1a523375c2500b69)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=12c1898fa00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+7f067c796eee2acbc57a@syzkaller.appspotmail.com

IPv6: ADDRCONF(NETDEV_CHANGE): hsr0: link becomes ready
8021q: adding VLAN 0 to HW filter on device batadv0
==================================================================
BUG: KASAN: use-after-free in atomic_read
/./include/asm-generic/atomic-instrumented.h:26 [inline]
BUG: KASAN: use-after-free in membarrier_mm_sync_core_before_usermode
/./include/linux/sched/mm.h:365 [inline]
BUG: KASAN: use-after-free in finish_task_switch+0x331/0x550
/kernel/sched/core.c:3122
Read of size 4 at addr ffff88808e6c18f8 by task syz-executor.0/8218

CPU: 0 PID: 8218 Comm: syz-executor.0 Not tainted 5.2.0+ #34
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+0x1d8/0x2f8 /lib/dump_stack.c:113
print_address_description+0x75/0x5b0 /mm/kasan/report.c:351
__kasan_report+0x14b/0x1c0 /mm/kasan/report.c:482
kasan_report+0x26/0x50 /mm/kasan/common.c:612
check_memory_region_inline /mm/kasan/generic.c:182 [inline]
check_memory_region+0x2cf/0x2e0 /mm/kasan/generic.c:192
__kasan_check_read+0x11/0x20 /mm/kasan/common.c:92
atomic_read /./include/asm-generic/atomic-instrumented.h:26 [inline]
membarrier_mm_sync_core_before_usermode /./include/linux/sched/mm.h:365
[inline]
finish_task_switch+0x331/0x550 /kernel/sched/core.c:3122
context_switch /kernel/sched/core.c:3257 [inline]
__schedule+0x8be/0xcd0 /kernel/sched/core.c:3880
schedule+0x131/0x1e0 /kernel/sched/core.c:3944
freezable_schedule /./include/linux/freezer.h:172 [inline]
do_nanosleep+0x295/0x7d0 /kernel/time/hrtimer.c:1679
hrtimer_nanosleep+0x3c2/0x5d0 /kernel/time/hrtimer.c:1733
__do_sys_nanosleep /kernel/time/hrtimer.c:1767 [inline]
__se_sys_nanosleep /kernel/time/hrtimer.c:1754 [inline]
__x64_sys_nanosleep+0x1ef/0x230 /kernel/time/hrtimer.c:1754
do_syscall_64+0xfe/0x140 /arch/x86/entry/common.c:296
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x457cc0
Code: c0 5b 5d c3 66 0f 1f 44 00 00 8b 04 24 48 83 c4 18 5b 5d c3 66 0f 1f
44 00 00 83 3d 91 ea 61 00 00 75 14 b8 23 00 00 00 0f 05 <48> 3d 01 f0 ff
ff 0f 83 24 d3 fb ff c3 48 83 ec 08 e8 ea 46 00 00
RSP: 002b:00007ffc89355738 EFLAGS: 00000246 ORIG_RAX: 0000000000000023
RAX: ffffffffffffffda RBX: 000000000000ea43 RCX: 0000000000457cc0
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00007ffc89355740
RBP: 000000000000000b R08: 0000000000000001 R09: 00005555559bf940
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000007
R13: 00007ffc89355790 R14: 000000000000e9c0 R15: 00007ffc893557a0

Allocated by task 8218:
save_stack /mm/kasan/common.c:69 [inline]
set_track /mm/kasan/common.c:77 [inline]
__kasan_kmalloc+0x11c/0x1b0 /mm/kasan/common.c:487
kasan_slab_alloc+0xf/0x20 /mm/kasan/common.c:495
slab_post_alloc_hook /mm/slab.h:520 [inline]
slab_alloc /mm/slab.c:3319 [inline]
kmem_cache_alloc+0x1f5/0x2e0 /mm/slab.c:3483
dup_mm+0x29/0x340 /kernel/fork.c:1337
copy_mm /kernel/fork.c:1402 [inline]
copy_process+0x25ef/0x5bc0 /kernel/fork.c:2017
_do_fork+0x179/0x630 /kernel/fork.c:2369
__do_sys_clone /kernel/fork.c:2524 [inline]
__se_sys_clone /kernel/fork.c:2505 [inline]
__x64_sys_clone+0x247/0x2b0 /kernel/fork.c:2505
do_syscall_64+0xfe/0x140 /arch/x86/entry/common.c:296
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 8244:
save_stack /mm/kasan/common.c:69 [inline]
set_track /mm/kasan/common.c:77 [inline]
__kasan_slab_free+0x12a/0x1e0 /mm/kasan/common.c:449
kasan_slab_free+0xe/0x10 /mm/kasan/common.c:457
__cache_free /mm/slab.c:3425 [inline]
kmem_cache_free+0x81/0xf0 /mm/slab.c:3693
__mmdrop+0x2c4/0x3b0 /kernel/fork.c:683
mmdrop /./include/linux/sched/mm.h:49 [inline]
__mmput+0x373/0x3a0 /kernel/fork.c:1074
mmput+0x5d/0x70 /kernel/fork.c:1085
exit_mm+0x585/0x640 /kernel/exit.c:547
do_exit+0x5d0/0x2310 /kernel/exit.c:864
do_group_exit+0x15c/0x2b0 /kernel/exit.c:981
get_signal+0x51c/0x1dd0 /kernel/signal.c:2728
do_signal+0x7b/0x720 /arch/x86/kernel/signal.c:815
exit_to_usermode_loop /arch/x86/entry/common.c:159 [inline]
prepare_exit_to_usermode+0x303/0x580 /arch/x86/entry/common.c:194
syscall_return_slowpath+0x113/0x4a0 /arch/x86/entry/common.c:274
do_syscall_64+0x126/0x140 /arch/x86/entry/common.c:299
entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff88808e6c1400
which belongs to the cache mm_struct(17:syz0) of size 1496
The buggy address is located 1272 bytes inside of
1496-byte region [ffff88808e6c1400, ffff88808e6c19d8)
The buggy address belongs to the page:
page:ffffea000239b000 refcount:1 mapcount:0 mapping:ffff8880867de8c0
index:0x0 compound_mapcount: 0
flags: 0x1fffc0000010200(slab|head)
raw: 01fffc0000010200 ffffea0002331108 ffff8880a380ff48 ffff8880867de8c0
raw: 0000000000000000 ffff88808e6c0080 0000000100000004 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff88808e6c1780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88808e6c1800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff88808e6c1880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88808e6c1900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88808e6c1980: fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc fc
==================================================================


---
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