KASAN: use-after-free Read in lo_ioctl

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: a0eae55f26a0 BACKPORT: mm: don't be stuck to rmap lock on ..
git tree: android12-5.4
console output: https://syzkaller.appspot.com/x/log.txt?x=1288d619480000
kernel config: https://syzkaller.appspot.com/x/.config?x=b4f7fdc1fca3154e
dashboard link: https://syzkaller.appspot.com/bug?extid=04ffca5a409f5a9255e3
compiler: Debian clang version 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, GNU ld (GNU Binutils for Debian) 2.35.2

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/f1c9555818f9/disk-a0eae55f.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/91f9c89de606/vmlinux-a0eae55f.xz
kernel image: https://storage.googleapis.com/syzbot-assets/9f867c3342d9/bzImage-a0eae55f.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+04ffca...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in mutex_spin_on_owner+0x2a6/0x310 kernel/locking/mutex.c:580
Read of size 4 at addr ffff8881ca97bf38 by task syz-executor.1/316

CPU: 1 PID: 316 Comm: syz-executor.1 Not tainted 5.4.219-syzkaller-00002-ga0eae55f26a0 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x1d8/0x241 lib/dump_stack.c:118
print_address_description+0x8c/0x630 mm/kasan/report.c:384
__kasan_report+0xf6/0x130 mm/kasan/report.c:516
kasan_report+0x30/0x60 mm/kasan/common.c:653
mutex_spin_on_owner+0x2a6/0x310 kernel/locking/mutex.c:580
mutex_optimistic_spin kernel/locking/mutex.c:685 [inline]
__mutex_lock_common kernel/locking/mutex.c:1063 [inline]
__mutex_lock+0x7c5/0x10d0 kernel/locking/mutex.c:1114
mutex_lock_killable+0xd9/0x120 kernel/locking/mutex.c:1348
loop_clr_fd drivers/block/loop.c:1321 [inline]
lo_ioctl+0x2b8/0x2310 drivers/block/loop.c:1709
__blkdev_driver_ioctl block/ioctl.c:304 [inline]
blkdev_ioctl+0x8d7/0x2cc0 block/ioctl.c:609
block_ioctl+0xa8/0xe0 fs/block_dev.c:1974
do_vfs_ioctl+0x744/0x1730 fs/ioctl.c:47
ksys_ioctl fs/ioctl.c:742 [inline]
__do_sys_ioctl fs/ioctl.c:749 [inline]
__se_sys_ioctl fs/ioctl.c:747 [inline]
__x64_sys_ioctl+0xd4/0x110 fs/ioctl.c:747
do_syscall_64+0xcb/0x1c0 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x5c/0xc1

Allocated by task 9352:
save_stack mm/kasan/common.c:70 [inline]
set_track mm/kasan/common.c:78 [inline]
__kasan_kmalloc+0x131/0x1e0 mm/kasan/common.c:529
slab_post_alloc_hook mm/slab.h:584 [inline]
slab_alloc_node mm/slub.c:2829 [inline]
slab_alloc mm/slub.c:2837 [inline]
kmem_cache_alloc+0xd0/0x210 mm/slub.c:2842
kmem_cache_alloc_node include/linux/slab.h:427 [inline]
alloc_task_struct_node kernel/fork.c:171 [inline]
dup_task_struct+0x4f/0x5a0 kernel/fork.c:871
copy_process+0x56e/0x3230 kernel/fork.c:1878
_do_fork+0x196/0x8d0 kernel/fork.c:2391
__do_sys_clone kernel/fork.c:2549 [inline]
__se_sys_clone kernel/fork.c:2530 [inline]
__x64_sys_clone+0x287/0x2f0 kernel/fork.c:2530
do_syscall_64+0xcb/0x1c0 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x5c/0xc1

Freed by task 155:
save_stack mm/kasan/common.c:70 [inline]
set_track mm/kasan/common.c:78 [inline]
kasan_set_free_info mm/kasan/common.c:345 [inline]
__kasan_slab_free+0x178/0x240 mm/kasan/common.c:487
slab_free_hook mm/slub.c:1455 [inline]
slab_free_freelist_hook+0x80/0x150 mm/slub.c:1494
slab_free mm/slub.c:3080 [inline]
kmem_cache_free+0xa9/0x1d0 mm/slub.c:3096
__rcu_reclaim kernel/rcu/rcu.h:222 [inline]
rcu_do_batch+0x49e/0xa10 kernel/rcu/tree.c:2167
rcu_core+0x4ba/0xca0 kernel/rcu/tree.c:2387
__do_softirq+0x23e/0x643 kernel/softirq.c:292

The buggy address belongs to the object at ffff8881ca97bf00
which belongs to the cache task_struct of size 3904
The buggy address is located 56 bytes inside of
3904-byte region [ffff8881ca97bf00, ffff8881ca97ce40)
The buggy address belongs to the page:
page:ffffea00072a5e00 refcount:1 mapcount:0 mapping:ffff8881f5cec500 index:0xffff8881ca97af40 compound_mapcount: 0
flags: 0x8000000000010200(slab|head)
raw: 8000000000010200 dead000000000100 dead000000000122 ffff8881f5cec500
raw: ffff8881ca97af40 0000000080080007 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0x1d20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_HARDWALL)
set_page_owner include/linux/page_owner.h:31 [inline]
post_alloc_hook mm/page_alloc.c:2165 [inline]
prep_new_page+0x194/0x380 mm/page_alloc.c:2171
get_page_from_freelist+0x524/0x560 mm/page_alloc.c:3794
__alloc_pages_nodemask+0x372/0x860 mm/page_alloc.c:4891
alloc_slab_page+0x39/0x3e0 mm/slub.c:343
allocate_slab mm/slub.c:1683 [inline]
new_slab+0x97/0x450 mm/slub.c:1749
new_slab_objects mm/slub.c:2505 [inline]
___slab_alloc+0x320/0x4a0 mm/slub.c:2667
__slab_alloc+0x5a/0x90 mm/slub.c:2707
slab_alloc_node mm/slub.c:2792 [inline]
slab_alloc mm/slub.c:2837 [inline]
kmem_cache_alloc+0x100/0x210 mm/slub.c:2842
kmem_cache_alloc_node include/linux/slab.h:427 [inline]
alloc_task_struct_node kernel/fork.c:171 [inline]
dup_task_struct+0x4f/0x5a0 kernel/fork.c:871
copy_process+0x56e/0x3230 kernel/fork.c:1878
_do_fork+0x196/0x8d0 kernel/fork.c:2391
__do_sys_clone kernel/fork.c:2549 [inline]
__se_sys_clone kernel/fork.c:2530 [inline]
__x64_sys_clone+0x287/0x2f0 kernel/fork.c:2530
do_syscall_64+0xcb/0x1c0 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x5c/0xc1
page last free stack trace:
reset_page_owner include/linux/page_owner.h:24 [inline]
free_pages_prepare mm/page_alloc.c:1176 [inline]
__free_pages_ok+0x7fe/0x930 mm/page_alloc.c:1438
free_the_page mm/page_alloc.c:4953 [inline]
__free_pages+0x8f/0x250 mm/page_alloc.c:4959
free_thread_stack kernel/fork.c:299 [inline]
release_task_stack kernel/fork.c:439 [inline]
put_task_stack+0x21a/0x270 kernel/fork.c:450
finish_task_switch+0x248/0x560 kernel/sched/core.c:3476
context_switch kernel/sched/core.c:3608 [inline]
__schedule+0x98e/0x1050 kernel/sched/core.c:4305
preempt_schedule_common+0x93/0xe0 kernel/sched/core.c:4454
preempt_schedule+0xd9/0xe0 kernel/sched/core.c:4479
___preempt_schedule+0x16/0x20 arch/x86/entry/thunk_64.S:50
try_to_wake_up+0xab2/0x1190 kernel/sched/core.c:2861
wake_up_process kernel/sched/core.c:2879 [inline]
wake_up_q+0xa3/0x100 kernel/sched/core.c:502
futex_wake+0x600/0x820 kernel/futex.c:1724
do_futex+0x13f4/0x19c0 kernel/futex.c:3893
__do_sys_futex kernel/futex.c:3949 [inline]
__se_sys_futex+0x34c/0x470 kernel/futex.c:3917
do_syscall_64+0xcb/0x1c0 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x5c/0xc1

Memory state around the buggy address:
ffff8881ca97be00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8881ca97be80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8881ca97bf00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff8881ca97bf80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8881ca97c000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


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[syzbot]

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