[syzbot] [kernfs?] KASAN: slab-use-after-free Read in __kernfs_new_node

[syzbot <syzbot+3942dc5563ea8b96bbbe@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    c425609d6ac4 Add linux-next specific files for 20260612
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=171a0bd2580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=d7a56b1e89b63439
dashboard link: https://syzkaller.appspot.com/bug?extid=3942dc5563ea8b96bbbe
compiler:       Debian clang version 22.1.6 (++20260514074242+fc4aad7b5db3-1~exp1~20260514074407.73), Debian LLD 22.1.6

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/7fab9a8df61a/disk-c425609d.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/c2577196651b/vmlinux-c425609d.xz
kernel image: https://storage.googleapis.com/syzbot-assets/053557a7471e/bzImage-c425609d.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+3942dc5563ea8b96bbbe@syzkaller.appspotmail.com

=========================================[  553.259716][   T10] ==================================================================
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 fs/kernfs/dir.c:560 [inline]
BUG: KASAN: slab-use-after-free in __kernfs_new_node+0x563/0xa70 fs/kernfs/dir.c:704
Read of size 4 at addr ffff88802991b4b0 by task kworker/0:1/10

CPU: 0 UID: 0 PID: 10 Comm: kworker/0:1 Tainted: G             L      syzkaller #0 PREEMPT_{RT,(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 fs/kernfs/dir.c:560 [inline]
 __kernfs_new_node+0x563/0xa70 fs/kernfs/dir.c:704
 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+0x62c/0xce0 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+0x31d/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+0x93a/0x12b0 kernel/workqueue.c:3326
 process_scheduled_works kernel/workqueue.c:3409 [inline]
 worker_thread+0xb05/0x10d0 kernel/workqueue.c:3490
 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 5753:
 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:4610 [inline]
 slab_alloc_node mm/slub.c:4943 [inline]
 kmem_cache_alloc_noprof+0x348/0x6b0 mm/slub.c:4957
 __kernfs_new_node+0xe7/0xa70 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+0x62c/0xce0 lib/kobject.c:240
 kobject_add_varg lib/kobject.c:374 [inline]
 kobject_add+0x163/0x240 lib/kobject.c:426
 device_add+0x3fa/0xb80 drivers/base/core.c:3695
 usb_new_device+0x98d/0x1610 drivers/usb/core/hub.c:2695
 hub_port_connect drivers/usb/core/hub.c:5567 [inline]
 hub_port_connect_change drivers/usb/core/hub.c:5707 [inline]
 port_event drivers/usb/core/hub.c:5871 [inline]
 hub_event+0x28cf/0x4cf0 drivers/usb/core/hub.c:5953
 process_one_work+0x93a/0x12b0 kernel/workqueue.c:3326
 process_scheduled_works kernel/workqueue.c:3409 [inline]
 worker_thread+0xb05/0x10d0 kernel/workqueue.c:3490
 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 29:
 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:2703 [inline]
 slab_free mm/slub.c:6402 [inline]
 kmem_cache_free+0x187/0x6c0 mm/slub.c:6529
 rcu_do_batch kernel/rcu/tree.c:2645 [inline]
 rcu_core kernel/rcu/tree.c:2897 [inline]
 rcu_cpu_kthread+0x950/0x1480 kernel/rcu/tree.c:2985
 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+0x625/0x820 fs/kernfs/dir.c:618
 evict+0x624/0xb50 fs/inode.c:825
 dentry_kill+0x1b9/0x880 fs/dcache.c:826
 finish_dput+0x1a/0x260 fs/dcache.c:1001
 lookup_fast+0x3d0/0x5d0 fs/namei.c:1886
 walk_component fs/namei.c:2278 [inline]
 link_path_walk+0x71f/0x1910 fs/namei.c:2656
 path_openat+0x23c/0x3850 fs/namei.c:4855
 do_file_open+0x23e/0x4a0 fs/namei.c:4888
 do_sys_openat2+0x115/0x200 fs/open.c:1368
 do_sys_open fs/open.c:1374 [inline]
 __do_sys_openat fs/open.c:1390 [inline]
 __se_sys_openat fs/open.c:1385 [inline]
 __x64_sys_openat+0x138/0x170 fs/open.c:1385
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff88802991b4b0
 which belongs to the cache kernfs_node_cache of size 176
The buggy address is located 0 bytes inside of
 freed 176-byte region [ffff88802991b4b0, ffff88802991b560)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x2991b
flags: 0x80000000000000(node=0|zone=1)
page_type: f5(slab)
raw: 0080000000000000 ffff88801be88b40 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 9436, tgid 9436 (syz-executor), ts 355931337322, free_ts 355813181360
 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+0x2639/0x26b0 mm/page_alloc.c:3946
 __alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5304
 alloc_slab_page mm/slub.c:3292 [inline]
 allocate_slab+0x79/0x5e0 mm/slub.c:3406
 new_slab mm/slub.c:3452 [inline]
 refill_objects+0x2d8/0x350 mm/slub.c:7335
 refill_sheaf mm/slub.c:2830 [inline]
 __pcs_replace_empty_main+0x330/0x690 mm/slub.c:4701
 alloc_from_pcs mm/slub.c:4799 [inline]
 slab_alloc_node mm/slub.c:4931 [inline]
 kmem_cache_alloc_noprof+0x465/0x6b0 mm/slub.c:4957
 __kernfs_new_node+0xe7/0xa70 fs/kernfs/dir.c:665
 kernfs_new_node+0xea/0x140 fs/kernfs/dir.c:751
 __kernfs_create_file+0x4b/0x2e0 fs/kernfs/file.c:1050
 sysfs_add_file_mode_ns+0x237/0x300 fs/sysfs/file.c:316
 create_files fs/sysfs/group.c:82 [inline]
 internal_create_group+0x679/0x1180 fs/sysfs/group.c:189
 internal_create_groups fs/sysfs/group.c:229 [inline]
 sysfs_create_groups+0x59/0x120 fs/sysfs/group.c:255
 netdev_queue_add_kobject net/core/net-sysfs.c:1982 [inline]
 netdev_queue_update_kobjects+0x2a4/0x6b0 net/core/net-sysfs.c:2035
 register_queue_kobjects net/core/net-sysfs.c:2098 [inline]
 netdev_register_kobject+0x258/0x310 net/core/net-sysfs.c:2341
 register_netdevice+0x1455/0x1ed0 net/core/dev.c:11437
page last free pid 21 tgid 21 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 __free_pages_prepare mm/page_alloc.c:1406 [inline]
 __free_frozen_pages+0x10de/0x11c0 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 kernel/rcu/tree.c:2897 [inline]
 rcu_cpu_kthread+0x950/0x1480 kernel/rcu/tree.c:2985
 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:
 ffff88802991b380: fc fc fc fc fc fc fc fc fa fb fb fb fb fb fb fb
 ffff88802991b400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fc fc
>ffff88802991b480: fc fc fc fc fc fc fa fb fb fb fb fb fb fb fb fb
                                     ^
 ffff88802991b500: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
 ffff88802991b580: fc fc fc fc 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================


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