[moderation] [kernfs?] KASAN: slab-use-after-free Read in kernfs_get (3)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 9845cf73f7db Add linux-next specific files for 20260205
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=17864a52580000
kernel config: https://syzkaller.appspot.com/x/.config?x=c09aefae2687abea
dashboard link: https://syzkaller.appspot.com/bug?extid=62a365def2038440b0b6
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
CC: [drive...@lists.linux.dev gre...@linuxfoundation.org linux-...@vger.kernel.org t...@kernel.org]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/52283f53ac01/disk-9845cf73.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/6f4eb10cc5fa/vmlinux-9845cf73.xz
kernel image: https://storage.googleapis.com/syzbot-assets/6b4c3f21179f/bzImage-9845cf73.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+62a365...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-use-after-free in instrument_atomic_read include/linux/instrumented.h:82 [inline]
BUG: KASAN: slab-use-after-free in atomic_read include/linux/atomic/atomic-instrumented.h:32 [inline]
BUG: KASAN: slab-use-after-free in kernfs_get+0x20/0x90 fs/kernfs/dir.c:537
Read of size 4 at addr ffff88803c32e5a0 by task kworker/1:8/5947

CPU: 1 UID: 0 PID: 5947 Comm: kworker/1:8 Tainted: G L syzkaller #0 PREEMPT(full)
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026
Workqueue: events update_super_work
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
print_address_description mm/kasan/report.c:378 [inline]
print_report+0xba/0x230 mm/kasan/report.c:482
kasan_report+0x117/0x150 mm/kasan/report.c:595
check_region_inline mm/kasan/generic.c:-1 [inline]
kasan_check_range+0x264/0x2c0 mm/kasan/generic.c:200
instrument_atomic_read include/linux/instrumented.h:82 [inline]
atomic_read include/linux/atomic/atomic-instrumented.h:32 [inline]
kernfs_get+0x20/0x90 fs/kernfs/dir.c:537
sysfs_notify+0x5a/0xe0 fs/sysfs/file.c:205
process_one_work+0x949/0x1650 kernel/workqueue.c:3279
process_scheduled_works kernel/workqueue.c:3362 [inline]
worker_thread+0xb46/0x1140 kernel/workqueue.c:3443
kthread+0x388/0x470 kernel/kthread.c:467
ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>

Allocated by task 8826:
kasan_save_stack mm/kasan/common.c:57 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
unpoison_slab_object mm/kasan/common.c:340 [inline]
__kasan_slab_alloc+0x6c/0x80 mm/kasan/common.c:366
kasan_slab_alloc include/linux/kasan.h:253 [inline]
slab_post_alloc_hook mm/slub.c:4456 [inline]
slab_alloc_node mm/slub.c:4785 [inline]
kmem_cache_alloc_noprof+0x2bc/0x650 mm/slub.c:4792
__kernfs_new_node+0xe9/0x8e0 fs/kernfs/dir.c:637
kernfs_new_node+0x102/0x210 fs/kernfs/dir.c:718
kernfs_create_dir_ns+0x44/0x130 fs/kernfs/dir.c:1088
sysfs_create_dir_ns+0x12f/0x2a0 fs/sysfs/dir.c:59
create_dir lib/kobject.c:73 [inline]
kobject_add_internal+0x62b/0xd00 lib/kobject.c:240
kobject_add_varg lib/kobject.c:374 [inline]
kobject_init_and_add+0x12b/0x1a0 lib/kobject.c:457
ext4_register_sysfs+0xae/0x2a0 fs/ext4/sysfs.c:613
__ext4_fill_super fs/ext4/super.c:5708 [inline]
ext4_fill_super+0x5daf/0x6320 fs/ext4/super.c:5793
get_tree_bdev_flags+0x431/0x4f0 fs/super.c:1694
vfs_get_tree+0x92/0x2a0 fs/super.c:1754
fc_mount fs/namespace.c:1193 [inline]
do_new_mount_fc fs/namespace.c:3760 [inline]
do_new_mount+0x341/0xd30 fs/namespace.c:3836
do_mount fs/namespace.c:4159 [inline]
__do_sys_mount fs/namespace.c:4348 [inline]
__se_sys_mount+0x31d/0x420 fs/namespace.c:4325
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 5188:
kasan_save_stack mm/kasan/common.c:57 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:584
poison_slab_object mm/kasan/common.c:253 [inline]
__kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285
kasan_slab_free include/linux/kasan.h:235 [inline]
slab_free_hook mm/slub.c:2667 [inline]
slab_free mm/slub.c:6079 [inline]
kmem_cache_free+0x187/0x630 mm/slub.c:6209
rcu_do_batch kernel/rcu/tree.c:2617 [inline]
rcu_core+0x7cd/0x1070 kernel/rcu/tree.c:2869
handle_softirqs+0x22a/0x870 kernel/softirq.c:626
do_softirq+0x76/0xd0 kernel/softirq.c:523
__local_bh_enable_ip+0xf8/0x130 kernel/softirq.c:450
local_bh_enable include/linux/bottom_half.h:33 [inline]
__alloc_skb+0x1aa/0x7d0 net/core/skbuff.c:697
netlink_sendmsg+0x5d4/0xb40 net/netlink/af_netlink.c:1869
sock_sendmsg_nosec+0x18f/0x1d0 net/socket.c:737
__sock_sendmsg net/socket.c:752 [inline]
____sys_sendmsg+0x589/0x8c0 net/socket.c:2610
___sys_sendmsg+0x2a5/0x360 net/socket.c:2664
__sys_sendmsg net/socket.c:2696 [inline]
__do_sys_sendmsg net/socket.c:2701 [inline]
__se_sys_sendmsg net/socket.c:2699 [inline]
__x64_sys_sendmsg+0x1bd/0x2a0 net/socket.c:2699
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Last potentially related work creation:
kasan_save_stack+0x3e/0x60 mm/kasan/common.c:57
kasan_record_aux_stack+0xbd/0xd0 mm/kasan/generic.c:556
__call_rcu_common kernel/rcu/tree.c:3131 [inline]
call_rcu+0xee/0x890 kernel/rcu/tree.c:3251
kernfs_put+0x18e/0x470 fs/kernfs/dir.c:591
sysfs_put include/linux/sysfs.h:808 [inline]
__kobject_del+0xe9/0x330 lib/kobject.c:605
kobject_del+0x45/0x60 lib/kobject.c:627
ext4_put_super+0x74/0xc40 fs/ext4/super.c:1297
generic_shutdown_super+0x13d/0x2d0 fs/super.c:646
kill_block_super+0x44/0x90 fs/super.c:1725
ext4_kill_sb+0x68/0xb0 fs/ext4/super.c:7461
deactivate_locked_super+0xbc/0x130 fs/super.c:476
cleanup_mnt+0x437/0x4d0 fs/namespace.c:1312
task_work_run+0x1d9/0x270 kernel/task_work.c:233
resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
__exit_to_user_mode_loop kernel/entry/common.c:67 [inline]
exit_to_user_mode_loop+0xed/0x480 kernel/entry/common.c:98
__exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline]
syscall_exit_to_user_mode include/linux/entry-common.h:325 [inline]
do_syscall_64+0x32d/0xf80 arch/x86/entry/syscall_64.c:100
entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff88803c32e5a0
which belongs to the cache kernfs_node_cache of size 176
The buggy address is located 0 bytes inside of
freed 176-byte region [ffff88803c32e5a0, ffff88803c32e650)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x3c32e
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000000 ffff888140413780 dead000000000100 dead000000000122
raw: 0000000000000000 0000000000110011 00000000f5000000 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0xd2cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 49, tgid 49 (kworker/u8:3), ts 378540699385, free_ts 377415198550
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x231/0x280 mm/page_alloc.c:1883
prep_new_page mm/page_alloc.c:1891 [inline]
get_page_from_freelist+0x24dc/0x2580 mm/page_alloc.c:3956
__alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5244
alloc_slab_page mm/slub.c:3235 [inline]
allocate_slab+0x7b/0x660 mm/slub.c:3408
new_slab mm/slub.c:3466 [inline]
refill_objects+0x331/0x3c0 mm/slub.c:7088
refill_sheaf mm/slub.c:2784 [inline]
__pcs_replace_empty_main+0x2b9/0x620 mm/slub.c:4533
alloc_from_pcs mm/slub.c:4636 [inline]
slab_alloc_node mm/slub.c:4770 [inline]
kmem_cache_alloc_noprof+0x37d/0x650 mm/slub.c:4792
__kernfs_new_node+0xe9/0x8e0 fs/kernfs/dir.c:637
kernfs_new_node+0x102/0x210 fs/kernfs/dir.c:718
__kernfs_create_file+0x4b/0x2e0 fs/kernfs/file.c:1057
sysfs_add_file_mode_ns+0x238/0x300 fs/sysfs/file.c:313
create_files fs/sysfs/group.c:82 [inline]
internal_create_group+0x673/0x1180 fs/sysfs/group.c:189
internal_create_groups fs/sysfs/group.c:229 [inline]
sysfs_create_groups+0x59/0x120 fs/sysfs/group.c:255
device_add_groups drivers/base/core.c:2836 [inline]
device_add_attrs+0xdd/0x5b0 drivers/base/core.c:2900
device_add+0x496/0xb70 drivers/base/core.c:3643
netdev_register_kobject+0x178/0x310 net/core/net-sysfs.c:2358
page last free pid 5838 tgid 5838 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
free_pages_prepare mm/page_alloc.c:1432 [inline]
free_unref_folios+0xd38/0x14c0 mm/page_alloc.c:3034
folios_put_refs+0x789/0x8d0 mm/swap.c:1002
folio_batch_release include/linux/pagevec.h:101 [inline]
truncate_inode_pages_range+0x3dd/0xe30 mm/truncate.c:408
kill_bdev block/bdev.c:91 [inline]
blkdev_flush_mapping+0x109/0x2f0 block/bdev.c:728
blkdev_put_whole block/bdev.c:735 [inline]
bdev_release+0x417/0x650 block/bdev.c:1160
blkdev_release+0x15/0x20 block/fops.c:706
__fput+0x44f/0xa70 fs/file_table.c:469
task_work_run+0x1d9/0x270 kernel/task_work.c:233
resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
__exit_to_user_mode_loop kernel/entry/common.c:67 [inline]
exit_to_user_mode_loop+0xed/0x480 kernel/entry/common.c:98
__exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline]
syscall_exit_to_user_mode include/linux/entry-common.h:325 [inline]
do_syscall_64+0x32d/0xf80 arch/x86/entry/syscall_64.c:100
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
ffff88803c32e480: fc fc fc fc fc fc fa fb fb fb fb fb fb fb fb fb
ffff88803c32e500: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
>ffff88803c32e580: fc fc fc fc fa fb fb fb fb fb fb fb fb fb fb fb
^
ffff88803c32e600: fb fb fb fb fb fb fb fb fb fb fc fc fc fc fc fc
ffff88803c32e680: fc fc 00 00 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================


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