[syzbot] [kernfs?] KASAN: slab-use-after-free Read in kernfs_get (4)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: d2c9a99135da Merge tag 'device-id-rework' of git://git.ker..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16dd80d6580000
kernel config: https://syzkaller.appspot.com/x/.config?x=5c4196ba0e33631d
dashboard link: https://syzkaller.appspot.com/bug?extid=61d22228f1d777d4a5c1
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/cb55a636c1b2/disk-d2c9a991.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/e4bdf13aafbf/vmlinux-d2c9a991.xz
kernel image: https://storage.googleapis.com/syzbot-assets/8388280f1b6e/bzImage-d2c9a991.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+61d222...@syzkaller.appspotmail.com

usb 4-1: Direct firmware load for ueagle-atm/eagleI.fw failed with error -2
usb 4-1: Falling back to sysfs fallback for: ueagle-atm/eagleI.fw
==================================================================
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:560
Read of size 4 at addr ffff8880338825a0 by task kworker/0:0/9

CPU: 0 UID: 0 PID: 9 Comm: kworker/0:0 Tainted: G L syzkaller #0 PREEMPT(full)
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
Workqueue: events request_firmware_work_func
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
print_address_description+0x55/0x1e0 mm/kasan/report.c:378
print_report+0x58/0x70 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:560
sysfs_get include/linux/sysfs.h:802 [inline]
create_dir lib/kobject.c:89 [inline]
kobject_add_internal+0x6b9/0xcd0 lib/kobject.c:240
kobject_add_varg lib/kobject.c:374 [inline]
kobject_add+0x163/0x240 lib/kobject.c:426
class_dir_create_and_add drivers/base/core.c:3300 [inline]
get_device_parent+0x316/0x3a0 drivers/base/core.c:3351
device_add+0x2d4/0xb80 drivers/base/core.c:3681
fw_load_sysfs_fallback drivers/base/firmware_loader/fallback.c:86 [inline]
fw_load_from_user_helper drivers/base/firmware_loader/fallback.c:162 [inline]
firmware_fallback_sysfs+0x2dd/0xa40 drivers/base/firmware_loader/fallback.c:238
_request_firmware+0x1049/0x1780 drivers/base/firmware_loader/main.c:898
request_firmware_work_func+0xac/0x2d0 drivers/base/firmware_loader/main.c:1162
process_one_work kernel/workqueue.c:3322 [inline]
process_scheduled_works+0xa8e/0x14e0 kernel/workqueue.c:3405
worker_thread+0xa47/0xfb0 kernel/workqueue.c:3486
kthread+0x388/0x470 kernel/kthread.c:436
ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>

Allocated by task 9:
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:4612 [inline]
slab_alloc_node mm/slub.c:4945 [inline]
kmem_cache_alloc_noprof+0x2a0/0x5f0 mm/slub.c:4959
__kernfs_new_node+0xe6/0x980 fs/kernfs/dir.c:665
kernfs_new_node fs/kernfs/dir.c:751 [inline]
kernfs_create_dir_ns+0xfe/0x230 fs/kernfs/dir.c:1120
sysfs_create_dir_ns+0x12f/0x2a0 fs/sysfs/dir.c:59
create_dir lib/kobject.c:73 [inline]
kobject_add_internal+0x622/0xcd0 lib/kobject.c:240
kobject_add_varg lib/kobject.c:374 [inline]
kobject_add+0x163/0x240 lib/kobject.c:426
class_dir_create_and_add drivers/base/core.c:3300 [inline]
get_device_parent+0x316/0x3a0 drivers/base/core.c:3351
device_add+0x2d4/0xb80 drivers/base/core.c:3681
fw_load_sysfs_fallback drivers/base/firmware_loader/fallback.c:86 [inline]
fw_load_from_user_helper drivers/base/firmware_loader/fallback.c:162 [inline]
firmware_fallback_sysfs+0x2dd/0xa40 drivers/base/firmware_loader/fallback.c:238
_request_firmware+0x1049/0x1780 drivers/base/firmware_loader/main.c:898
request_firmware_work_func+0xac/0x2d0 drivers/base/firmware_loader/main.c:1162
process_one_work kernel/workqueue.c:3322 [inline]
process_scheduled_works+0xa8e/0x14e0 kernel/workqueue.c:3405
worker_thread+0xa47/0xfb0 kernel/workqueue.c:3486
kthread+0x388/0x470 kernel/kthread.c:436
ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Freed by task 15:
kasan_save_stack mm/kasan/common.c:57 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
kasan_save_free_info+0x40/0x50 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:2705 [inline]
slab_free mm/slub.c:6405 [inline]
kmem_cache_free+0x182/0x650 mm/slub.c:6532
rcu_do_batch kernel/rcu/tree.c:2645 [inline]
rcu_core+0x78b/0x10a0 kernel/rcu/tree.c:2897
handle_softirqs+0x225/0x840 kernel/softirq.c:622
run_ksoftirqd+0x36/0x60 kernel/softirq.c:1076
smpboot_thread_fn+0x57c/0xa80 kernel/smpboot.c:160
kthread+0x388/0x470 kernel/kthread.c:436
ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

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:3159 [inline]
call_rcu+0xee/0x8b0 kernel/rcu/tree.c:3279
kernfs_put+0x622/0x820 fs/kernfs/dir.c:618
__kernfs_remove+0x69a/0x8e0 fs/kernfs/dir.c:1603
kernfs_remove+0x4c/0x80 fs/kernfs/dir.c:1624
__kobject_del+0xe0/0x310 lib/kobject.c:604
kobject_del+0x45/0x60 lib/kobject.c:627
device_del+0x772/0x8f0 drivers/base/core.c:3981
usb_disconnect+0x630/0x9a0 drivers/usb/core/hub.c:2376
hub_port_connect drivers/usb/core/hub.c:5407 [inline]
hub_port_connect_change drivers/usb/core/hub.c:5707 [inline]
port_event drivers/usb/core/hub.c:5871 [inline]
hub_event+0x1bbb/0x4d30 drivers/usb/core/hub.c:5953
process_one_work kernel/workqueue.c:3322 [inline]
process_scheduled_works+0xa8e/0x14e0 kernel/workqueue.c:3405
worker_thread+0xa47/0xfb0 kernel/workqueue.c:3486
kthread+0x388/0x470 kernel/kthread.c:436
ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

The buggy address belongs to the object at ffff8880338825a0
which belongs to the cache kernfs_node_cache of size 176
The buggy address is located 0 bytes inside of
freed 176-byte region [ffff8880338825a0, ffff888033882650)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x33882
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000000 ffff888140415280 dead000000000100 dead000000000122
raw: 0000000000000000 0000000800110011 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 8130, tgid 8129 (syz.0.763), ts 244206391995, free_ts 244188026758
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x1f9/0x250 mm/page_alloc.c:1859
prep_new_page mm/page_alloc.c:1867 [inline]
get_page_from_freelist+0x21fa/0x2270 mm/page_alloc.c:3946
__alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5304
alloc_slab_page mm/slub.c:3294 [inline]
allocate_slab+0x79/0x5e0 mm/slub.c:3408
new_slab mm/slub.c:3454 [inline]
refill_objects+0x2d5/0x350 mm/slub.c:7338
refill_sheaf mm/slub.c:2832 [inline]
__pcs_replace_empty_main+0x2bf/0x6b0 mm/slub.c:4703
alloc_from_pcs mm/slub.c:4801 [inline]
slab_alloc_node mm/slub.c:4933 [inline]
kmem_cache_alloc_noprof+0x382/0x5f0 mm/slub.c:4959
__kernfs_new_node+0xe6/0x980 fs/kernfs/dir.c:665
kernfs_new_node fs/kernfs/dir.c:751 [inline]
kernfs_create_dir_ns+0xfe/0x230 fs/kernfs/dir.c:1120
sysfs_create_dir_ns+0x12f/0x2a0 fs/sysfs/dir.c:59
create_dir lib/kobject.c:73 [inline]
kobject_add_internal+0x622/0xcd0 lib/kobject.c:240
kobject_add_varg lib/kobject.c:374 [inline]
kobject_init_and_add+0x12b/0x1a0 lib/kobject.c:457
rx_queue_add_kobject net/core/net-sysfs.c:1239 [inline]
net_rx_queue_update_kobjects+0x247/0x780 net/core/net-sysfs.c:1301
register_queue_kobjects net/core/net-sysfs.c:2093 [inline]
netdev_register_kobject+0x21f/0x310 net/core/net-sysfs.c:2341
register_netdevice+0x1433/0x1eb0 net/core/dev.c:11440
register_netdev+0x40/0x60 net/core/dev.c:11556
page last free pid 23 tgid 23 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
__free_pages_prepare mm/page_alloc.c:1406 [inline]
__free_frozen_pages+0xc1e/0xd10 mm/page_alloc.c:2950
__tlb_remove_table_free mm/mmu_gather.c:228 [inline]
tlb_remove_table_rcu+0x85/0x100 mm/mmu_gather.c:291
rcu_do_batch kernel/rcu/tree.c:2645 [inline]
rcu_core+0x78b/0x10a0 kernel/rcu/tree.c:2897
handle_softirqs+0x225/0x840 kernel/softirq.c:622
run_ksoftirqd+0x36/0x60 kernel/softirq.c:1076
smpboot_thread_fn+0x57c/0xa80 kernel/smpboot.c:160
kthread+0x388/0x470 kernel/kthread.c:436
ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Memory state around the buggy address:
ffff888033882480: fc fc fc fc fc fc fa fb fb fb fb fb fb fb fb fb
ffff888033882500: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
>ffff888033882580: fc fc fc fc fa fb fb fb fb fb fb fb fb fb fb fb
^
ffff888033882600: fb fb fb fb fb fb fb fb fb fb fc fc fc fc fc fc
ffff888033882680: fc fc fa fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


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