[v6.1] KASAN: use-after-free Read in kernfs_find_ns

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: fb28aa725e05 Linux 6.1.180
git tree: linux-6.1.y
console output: https://syzkaller.appspot.com/x/log.txt?x=1545ee32580000
kernel config: https://syzkaller.appspot.com/x/.config?x=31dfefc4a14efea3
dashboard link: https://syzkaller.appspot.com/bug?extid=dc2b9b6017fc273fee9a
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=171c2db9580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/9a6fe2a54d0f/disk-fb28aa72.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/742b23a1d931/vmlinux-fb28aa72.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b3f257c16d2e/bzImage-fb28aa72.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+dc2b9b...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in strlen+0x53/0x60 lib/string.c:502
Read of size 1 at addr ffff88813fe3d240 by task syz.3.263/5004

CPU: 0 PID: 5004 Comm: syz.3.263 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
<TASK>
dump_stack_lvl+0x188/0x24e lib/dump_stack.c:106
print_address_description mm/kasan/report.c:316 [inline]
print_report+0xa8/0x210 mm/kasan/report.c:420
kasan_report+0x10b/0x140 mm/kasan/report.c:524
strlen+0x53/0x60 lib/string.c:502
__fortify_strlen include/linux/fortify-string.h:196 [inline]
kernfs_name_hash fs/kernfs/dir.c:318 [inline]
kernfs_find_ns+0x12b/0x550 fs/kernfs/dir.c:840
kernfs_remove_by_name_ns+0x86/0x150 fs/kernfs/dir.c:1664
driver_sysfs_remove drivers/base/dd.c:475 [inline]
__device_release_driver drivers/base/dd.c:1270 [inline]
device_release_driver_internal+0x36c/0x7c0 drivers/base/dd.c:1305
bus_remove_device+0x2dd/0x400 drivers/base/bus.c:531
device_del+0x63f/0xa80 drivers/base/core.c:3900
usb_del_gadget+0x18c/0x250 drivers/usb/gadget/udc/core.c:1580
usb_del_gadget_udc+0x11/0x30 drivers/usb/gadget/udc/core.c:1603
dummy_udc_remove+0x54/0x60 drivers/usb/gadget/udc/dummy_hcd.c:1123
platform_remove+0x92/0xe0 drivers/base/platform.c:1422
device_remove drivers/base/dd.c:547 [inline]
__device_release_driver drivers/base/dd.c:1279 [inline]
device_release_driver_internal+0x47d/0x7c0 drivers/base/dd.c:1305
unbind_store+0x2e2/0x300 drivers/base/bus.c:193
kernfs_fop_write_iter+0x3a0/0x520 fs/kernfs/file.c:352
call_write_iter include/linux/fs.h:2265 [inline]
new_sync_write fs/read_write.c:491 [inline]
vfs_write+0x482/0x9a0 fs/read_write.c:584
ksys_write+0x14d/0x260 fs/read_write.c:637
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f7bd879e019
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f7bd7dfe028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f7bd8a25fa0 RCX: 00007f7bd879e019
RDX: 000000000000000b RSI: 0000200000000400 RDI: 0000000000000004
RBP: 00007f7bd883500c R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f7bd8a26038 R14: 00007f7bd8a25fa0 R15: 00007ffdedb815c8
</TASK>

Allocated by task 5002:
kasan_save_stack mm/kasan/common.c:46 [inline]
kasan_set_track+0x4b/0x70 mm/kasan/common.c:53
____kasan_kmalloc mm/kasan/common.c:375 [inline]
__kasan_kmalloc+0x8e/0xa0 mm/kasan/common.c:384
kasan_kmalloc include/linux/kasan.h:211 [inline]
__do_kmalloc_node mm/slab_common.c:936 [inline]
__kmalloc_node_track_caller+0xb0/0x240 mm/slab_common.c:956
kvasprintf+0xe8/0x1a0 lib/kasprintf.c:25
kobject_set_name_vargs+0x5d/0x110 lib/kobject.c:265
dev_set_name+0xdf/0x130 drivers/base/core.c:3485
usb_add_gadget+0x474/0x6f0 drivers/usb/gadget/udc/core.c:1448
usb_add_gadget_udc_release+0x198/0x1e0 drivers/usb/gadget/udc/core.c:1506
dummy_udc_probe+0x686/0x780 drivers/usb/gadget/udc/dummy_hcd.c:1102
platform_probe+0x137/0x1c0 drivers/base/platform.c:1400
call_driver_probe drivers/base/dd.c:-1 [inline]
really_probe+0x24a/0xb40 drivers/base/dd.c:638
__driver_probe_device+0x1f5/0x390 drivers/base/dd.c:804
device_driver_attach+0xd9/0x1c0 drivers/base/dd.c:1131
bind_store+0x33b/0x380 drivers/base/bus.c:216
kernfs_fop_write_iter+0x3a0/0x520 fs/kernfs/file.c:352
call_write_iter include/linux/fs.h:2265 [inline]
new_sync_write fs/read_write.c:491 [inline]
vfs_write+0x482/0x9a0 fs/read_write.c:584
ksys_write+0x14d/0x260 fs/read_write.c:637
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2

Freed by task 5004:
kasan_save_stack mm/kasan/common.c:46 [inline]
kasan_set_track+0x4b/0x70 mm/kasan/common.c:53
kasan_save_free_info+0x27/0x40 mm/kasan/generic.c:516
____kasan_slab_free+0x126/0x1f0 mm/kasan/common.c:237
kasan_slab_free include/linux/kasan.h:177 [inline]
slab_free_hook mm/slub.c:1729 [inline]
slab_free_freelist_hook+0x133/0x1b0 mm/slub.c:1755
slab_free mm/slub.c:3687 [inline]
__kmem_cache_free+0xb6/0x200 mm/slub.c:3700
kobject_cleanup lib/kobject.c:687 [inline]
kobject_release lib/kobject.c:712 [inline]
kref_put include/linux/kref.h:65 [inline]
kobject_put+0x25c/0x450 lib/kobject.c:729
bus_remove_device+0x2bf/0x400 drivers/base/bus.c:527
device_del+0x63f/0xa80 drivers/base/core.c:3900
usb_del_gadget+0x18c/0x250 drivers/usb/gadget/udc/core.c:1580
usb_del_gadget_udc+0x11/0x30 drivers/usb/gadget/udc/core.c:1603
dummy_udc_remove+0x54/0x60 drivers/usb/gadget/udc/dummy_hcd.c:1123
platform_remove+0x92/0xe0 drivers/base/platform.c:1422
device_remove drivers/base/dd.c:547 [inline]
__device_release_driver drivers/base/dd.c:1279 [inline]
device_release_driver_internal+0x47d/0x7c0 drivers/base/dd.c:1305
unbind_store+0x2e2/0x300 drivers/base/bus.c:193
kernfs_fop_write_iter+0x3a0/0x520 fs/kernfs/file.c:352
call_write_iter include/linux/fs.h:2265 [inline]
new_sync_write fs/read_write.c:491 [inline]
vfs_write+0x482/0x9a0 fs/read_write.c:584
ksys_write+0x14d/0x260 fs/read_write.c:637
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2

The buggy address belongs to the object at ffff88813fe3d240
which belongs to the cache kmalloc-16 of size 16
The buggy address is located 0 bytes inside of
16-byte region [ffff88813fe3d240, ffff88813fe3d250)

The buggy address belongs to the physical page:
page:ffffea0004ff8f40 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff88813fe3dc60 pfn:0x13fe3d
flags: 0x17ff00000000200(slab|node=0|zone=2|lastcpupid=0x7ff)
raw: 017ff00000000200 0000000000000000 dead000000000001 ffff8880174413c0
raw: ffff88813fe3dc60 000000008080007d 00000001ffffffff 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 0x0(), pid 1, tgid 1 (swapper/0), ts 2183073152, free_ts 0
create_dummy_stack mm/page_owner.c:67 [inline]
register_early_stack+0x95/0xf0 mm/page_owner.c:83
init_page_owner+0x2f/0x5b0 mm/page_owner.c:93
invoke_init_callbacks mm/page_ext.c:126 [inline]
page_ext_init+0x7f1/0x856 mm/page_ext.c:518
kernel_init_freeable+0x3fc/0x5ab init/main.c:1635
page_owner free stack trace missing

Memory state around the buggy address:
ffff88813fe3d100: fa fb fc fc fa fb fc fc fa fb fc fc 00 04 fc fc
ffff88813fe3d180: fa fb fc fc fa fb fc fc fa fb fc fc 00 05 fc fc
>ffff88813fe3d200: 00 01 fc fc 00 00 fc fc fa fb fc fc fa fb fc fc
^
ffff88813fe3d280: fb fb fc fc fa fb fc fc fa fb fc fc fa fb fc fc
ffff88813fe3d300: fa fb fc fc 00 01 fc fc fa fb fc fc fa fb fc fc
==================================================================


---
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