==================================================================
BUG: KASAN: use-after-free in atomic_fetch_add include/asm-generic/atomic-instrumented.h:111 [inline]
BUG: KASAN: use-after-free in refcount_add include/linux/refcount.h:188 [inline]
BUG: KASAN: use-after-free in refcount_inc include/linux/refcount.h:228 [inline]
BUG: KASAN: use-after-free in get_task_struct include/linux/sched/task.h:111 [inline]
BUG: KASAN: use-after-free in kthread_stop+0x37/0x4a0 kernel/kthread.c:612
Write of size 4 at addr ffff8881debd1fa0 by task syz-executor.4/318

CPU: 0 PID: 318 Comm: syz-executor.4 Not tainted 5.4.225-syzkaller-00008-g07edbcca3d39 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/02/2023
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1d8/0x241 lib/dump_stack.c:118
 print_address_description+0x8c/0x600 mm/kasan/report.c:384
 __kasan_report+0xf3/0x120 mm/kasan/report.c:516
 kasan_report+0x30/0x60 mm/kasan/common.c:653
 check_memory_region_inline mm/kasan/generic.c:141 [inline]
 check_memory_region+0x272/0x280 mm/kasan/generic.c:191
 atomic_fetch_add include/asm-generic/atomic-instrumented.h:111 [inline]
 refcount_add include/linux/refcount.h:188 [inline]
 refcount_inc include/linux/refcount.h:228 [inline]
 get_task_struct include/linux/sched/task.h:111 [inline]
 kthread_stop+0x37/0x4a0 kernel/kthread.c:612
 ext4_put_super+0x7a1/0xbc0 fs/ext4/super.c:1055
 generic_shutdown_super+0x121/0x2a0 fs/super.c:464
 kill_block_super+0x7a/0xe0 fs/super.c:1444
 deactivate_locked_super+0xa8/0x110 fs/super.c:335
 deactivate_super+0x1e2/0x2a0 fs/super.c:366
 cleanup_mnt+0x419/0x4d0 fs/namespace.c:1102
 task_work_run+0x140/0x170 kernel/task_work.c:113
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_usermode_loop+0x18b/0x1a0 arch/x86/entry/common.c:163
 prepare_exit_to_usermode+0x199/0x200 arch/x86/entry/common.c:194
 entry_SYSCALL_64_after_hwframe+0x5c/0xc1

Allocated by task 2:
 save_stack mm/kasan/common.c:70 [inline]
 set_track mm/kasan/common.c:78 [inline]
 __kasan_kmalloc+0x130/0x1d0 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+0xd0/0x220 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+0x56d/0x3230 kernel/fork.c:1878
 _do_fork+0x197/0x900 kernel/fork.c:2391
 kernel_thread+0x16a/0x1d0 kernel/fork.c:2481
 create_kthread kernel/kthread.c:311 [inline]
 kthreadd+0x3b1/0x4f0 kernel/kthread.c:654
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:354

Freed by task 9:
 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+0x178/0x230 mm/kasan/common.c:487
 slab_free_hook mm/slub.c:1455 [inline]
 slab_free_freelist_hook mm/slub.c:1494 [inline]
 slab_free mm/slub.c:3080 [inline]
 kmem_cache_free+0xd5/0x290 mm/slub.c:3096
 __rcu_reclaim kernel/rcu/rcu.h:222 [inline]
 rcu_do_batch+0x492/0xa00 kernel/rcu/tree.c:2167
 rcu_core+0x4c8/0xcb0 kernel/rcu/tree.c:2387
 __do_softirq+0x22e/0x630 kernel/softirq.c:292

The buggy address belongs to the object at ffff8881debd1f80
 which belongs to the cache task_struct of size 3904
The buggy address is located 32 bytes inside of
 3904-byte region [ffff8881debd1f80, ffff8881debd2ec0)
The buggy address belongs to the page:
page:ffffea00077af400 refcount:1 mapcount:0 mapping:ffff8881f5ced900 index:0x0 compound_mapcount: 0
flags: 0x8000000000010200(slab|head)
raw: 8000000000010200 ffffea00077af200 0000000600000006 ffff8881f5ced900
raw: 0000000000000000 0000000000080008 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 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC)
 set_page_owner include/linux/page_owner.h:31 [inline]
 post_alloc_hook mm/page_alloc.c:2165 [inline]
 prep_new_page+0x18f/0x370 mm/page_alloc.c:2171
 get_page_from_freelist+0x2ce8/0x2d70 mm/page_alloc.c:3794
 __alloc_pages_nodemask+0x393/0x840 mm/page_alloc.c:4891
 alloc_slab_page+0x39/0x3c0 mm/slub.c:343
 allocate_slab mm/slub.c:1683 [inline]
 new_slab+0x97/0x440 mm/slub.c:1749
 new_slab_objects mm/slub.c:2505 [inline]
 ___slab_alloc+0x2fe/0x490 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+0x100/0x220 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+0x56d/0x3230 kernel/fork.c:1878
 _do_fork+0x197/0x900 kernel/fork.c:2391
 __do_sys_clone kernel/fork.c:2549 [inline]
 __se_sys_clone kernel/fork.c:2530 [inline]
 __x64_sys_clone+0x26b/0x2c0 kernel/fork.c:2530
 do_syscall_64+0xca/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+0x83d/0x940 mm/page_alloc.c:1438
 free_the_page mm/page_alloc.c:4953 [inline]
 __free_pages+0x91/0x140 mm/page_alloc.c:4959
 free_thread_stack kernel/fork.c:299 [inline]
 release_task_stack kernel/fork.c:439 [inline]
 put_task_stack+0x212/0x260 kernel/fork.c:450
 finish_task_switch+0x241/0x560 kernel/sched/core.c:3476
 context_switch kernel/sched/core.c:3608 [inline]
 __schedule+0xb03/0x12a0 kernel/sched/core.c:4305
 schedule+0x12c/0x1d0 kernel/sched/core.c:4373
 schedule_timeout+0xa8/0x3d0 kernel/time/timer.c:1885
 freezable_schedule_timeout include/linux/freezer.h:192 [inline]
 unix_stream_data_wait net/unix/af_unix.c:2249 [inline]
 unix_stream_read_generic+0x1592/0x2060 net/unix/af_unix.c:2357
 unix_stream_recvmsg+0x166/0x1e0 net/unix/af_unix.c:2500
 sock_recvmsg_nosec net/socket.c:872 [inline]
 sock_recvmsg net/socket.c:890 [inline]
 sock_read_iter+0x34e/0x430 net/socket.c:968
 call_read_iter include/linux/fs.h:1975 [inline]
 new_sync_read fs/read_write.c:414 [inline]
 __vfs_read+0x5cd/0x730 fs/read_write.c:427
 vfs_read+0x148/0x360 fs/read_write.c:461
 ksys_read+0x199/0x2c0 fs/read_write.c:587
 do_syscall_64+0xca/0x1c0 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x5c/0xc1

Memory state around the buggy address:
 ffff8881debd1e80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff8881debd1f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8881debd1f80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                               ^
 ffff8881debd2000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8881debd2080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
------------[ cut here ]------------
refcount_t: addition on 0; use-after-free.
WARNING: CPU: 0 PID: 318 at lib/refcount.c:25 refcount_warn_saturate+0x132/0x1a0 lib/refcount.c:25
Modules linked in:
CPU: 0 PID: 318 Comm: syz-executor.4 Tainted: G    B             5.4.225-syzkaller-00008-g07edbcca3d39 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/02/2023
RIP: 0010:refcount_warn_saturate+0x132/0x1a0 lib/refcount.c:25
Code: 03 01 48 c7 c7 80 74 d9 84 e8 4a 9d 19 ff 0f 0b eb a9 e8 21 bb 41 ff c6 05 51 47 e3 03 01 48 c7 c7 00 75 d9 84 e8 2e 9d 19 ff <0f> 0b eb 8d e8 05 bb 41 ff c6 05 36 47 e3 03 01 48 c7 c7 60 75 d9
RSP: 0018:ffff8881b0f07c30 EFLAGS: 00010246
RAX: de50e30a296c5c00 RBX: 0000000000000002 RCX: ffff8881de84cec0
RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
RBP: 0000000000000002 R08: ffffffff814ca286 R09: 0000000000000003
R10: ffffffffffffffff R11: dffffc0000000001 R12: dffffc0000000000
R13: ffff8881debd1f80 R14: dffffc0000000000 R15: ffff8881debd1fa0
FS:  0000555555996400(0000) GS:ffff8881f6e00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000555555a47728 CR3: 00000001b0ec0000 CR4: 00000000003406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 refcount_add include/linux/refcount.h:192 [inline]
 refcount_inc include/linux/refcount.h:228 [inline]
 get_task_struct include/linux/sched/task.h:111 [inline]
 kthread_stop+0x1a5/0x4a0 kernel/kthread.c:612
 ext4_put_super+0x7a1/0xbc0 fs/ext4/super.c:1055
 generic_shutdown_super+0x121/0x2a0 fs/super.c:464
 kill_block_super+0x7a/0xe0 fs/super.c:1444
 deactivate_locked_super+0xa8/0x110 fs/super.c:335
 deactivate_super+0x1e2/0x2a0 fs/super.c:366
 cleanup_mnt+0x419/0x4d0 fs/namespace.c:1102
 task_work_run+0x140/0x170 kernel/task_work.c:113
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_usermode_loop+0x18b/0x1a0 arch/x86/entry/common.c:163
 prepare_exit_to_usermode+0x199/0x200 arch/x86/entry/common.c:194
 entry_SYSCALL_64_after_hwframe+0x5c/0xc1
---[ end trace 0d241f251c0d779b ]---