[syzbot] [fs?] KASAN: slab-use-after-free Write in config_item_get

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: fc02acf6ac0c Merge tag 'platform-drivers-x86-v7.2-4' of gi..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1220b1b9580000
kernel config: https://syzkaller.appspot.com/x/.config?x=cb17729fb04b1e3a
dashboard link: https://syzkaller.appspot.com/bug?extid=6b16e3d085833cbf3e25
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=121ea49e580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1620b1b9580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/b3bff1d63ddf/disk-fc02acf6.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/04efa97b7fb6/vmlinux-fc02acf6.xz
kernel image: https://storage.googleapis.com/syzbot-assets/be724b7ea80c/bzImage-fc02acf6.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+6b16e3...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-use-after-free in instrument_atomic_read_write include/linux/instrumented.h:112 [inline]
BUG: KASAN: slab-use-after-free in atomic_fetch_add_relaxed include/linux/atomic/atomic-instrumented.h:252 [inline]
BUG: KASAN: slab-use-after-free in __refcount_add include/linux/refcount.h:283 [inline]
BUG: KASAN: slab-use-after-free in __refcount_inc include/linux/refcount.h:366 [inline]
BUG: KASAN: slab-use-after-free in refcount_inc include/linux/refcount.h:383 [inline]
BUG: KASAN: slab-use-after-free in kref_get include/linux/kref.h:45 [inline]
BUG: KASAN: slab-use-after-free in config_item_get+0x26/0x90 fs/configfs/item.c:104
Write of size 4 at addr ffff888039f5201c by task syz.3.408/6784

CPU: 1 UID: 0 PID: 6784 Comm: syz.3.408 Not tainted syzkaller #0 PREEMPT_{RT,(full)}
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
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_write include/linux/instrumented.h:112 [inline]
atomic_fetch_add_relaxed include/linux/atomic/atomic-instrumented.h:252 [inline]
__refcount_add include/linux/refcount.h:283 [inline]
__refcount_inc include/linux/refcount.h:366 [inline]
refcount_inc include/linux/refcount.h:383 [inline]
kref_get include/linux/kref.h:45 [inline]
config_item_get+0x26/0x90 fs/configfs/item.c:104
configfs_get_config_item fs/configfs/configfs_internal.h:127 [inline]
get_target fs/configfs/symlink.c:128 [inline]
configfs_symlink+0x4ab/0x1030 fs/configfs/symlink.c:185
vfs_symlink+0x18b/0x330 fs/namei.c:5660
filename_symlinkat+0x1cd/0x420 fs/namei.c:5685
__do_sys_symlinkat fs/namei.c:5705 [inline]
__se_sys_symlinkat+0x4e/0x2b0 fs/namei.c:5700
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
RIP: 0033:0x7f98f891de99
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:00007f98f7f7e028 EFLAGS: 00000246 ORIG_RAX: 000000000000010a
RAX: ffffffffffffffda RBX: 00007f98f8ba5fa0 RCX: 00007f98f891de99
RDX: 0000200000000340 RSI: ffffffffffffff9c RDI: 0000200000000300
RBP: 00007f98f89b3eaf R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f98f8ba6038 R14: 00007f98f8ba5fa0 R15: 00007ffce9af1ce8
</TASK>

Allocated by task 6785:
kasan_save_stack mm/kasan/common.c:57 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
__kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:415
kasan_kmalloc include/linux/kasan.h:263 [inline]
__kmalloc_cache_noprof+0x3d2/0x6b0 mm/slub.c:5489
_kmalloc_noprof include/linux/slab.h:988 [inline]
_kzalloc_noprof include/linux/slab.h:1309 [inline]
afunc_alloc_inst+0x4c/0x770 drivers/usb/gadget/function/f_uac2.c:2192
try_get_usb_function_instance drivers/usb/gadget/functions.c:28 [inline]
usb_get_function_instance+0xe3/0x2f0 drivers/usb/gadget/functions.c:44
function_make+0x127/0x360 drivers/usb/gadget/configfs.c:626
configfs_mkdir+0x4f6/0x9e0 fs/configfs/dir.c:1360
vfs_mkdir+0x402/0x620 fs/namei.c:5276
filename_mkdirat+0x289/0x520 fs/namei.c:5309
__do_sys_mkdirat fs/namei.c:5330 [inline]
__se_sys_mkdirat+0x35/0x150 fs/namei.c:5327
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 ffff888039f52000
which belongs to the cache kmalloc-2k of size 2048
The buggy address is located 28 bytes inside of
freed 2048-byte region [ffff888039f52000, ffff888039f52800)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff888039f50000 pfn:0x39f50
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0x80000000000240(workingset|head|node=0|zone=1)
page_type: f5(slab)
raw: 0080000000000240 ffff88813ffb2000 ffffea0000d6de10 ffffea0000f10610
raw: ffff888039f50000 0000000800080005 00000000f5000000 0000000000000000
head: 0080000000000240 ffff88813ffb2000 ffffea0000d6de10 ffffea0000f10610
head: ffff888039f50000 0000000800080005 00000000f5000000 0000000000000000
head: 0080000000000003 fffffffffffffe01 00000000ffffffff 00000000ffffffff
head: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000008
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd2820(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 5743, tgid 5743 (syz-executor), ts 119768577290, free_ts 119599127308
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+0x262a/0x26a0 mm/page_alloc.c:3946
__alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5304
alloc_slab_page mm/slub.c:3266 [inline]
allocate_slab+0x79/0x5e0 mm/slub.c:3380
new_slab mm/slub.c:3426 [inline]
refill_objects+0x2d8/0x350 mm/slub.c:7310
refill_sheaf mm/slub.c:2804 [inline]
__pcs_replace_empty_main+0x330/0x690 mm/slub.c:4675
alloc_from_pcs mm/slub.c:4773 [inline]
slab_alloc_node mm/slub.c:4905 [inline]
__kmalloc_cache_noprof+0x468/0x6b0 mm/slub.c:5485
_kmalloc_noprof include/linux/slab.h:988 [inline]
_kzalloc_noprof include/linux/slab.h:1309 [inline]
batadv_hardif_add_interface net/batman-adv/hard-interface.c:878 [inline]
batadv_hard_if_event+0x282a/0x3530 net/batman-adv/hard-interface.c:1087
notifier_call_chain+0x1a5/0x3d0 kernel/notifier.c:85
call_netdevice_notifiers_extack net/core/dev.c:2288 [inline]
call_netdevice_notifiers net/core/dev.c:2302 [inline]
register_netdevice+0x18c0/0x1ed0 net/core/dev.c:11484
nsim_init_netdevsim drivers/net/netdevsim/netdev.c:1070 [inline]
nsim_create+0xbe9/0x1160 drivers/net/netdevsim/netdev.c:1152
__nsim_dev_port_add+0x7f8/0xcd0 drivers/net/netdevsim/dev.c:1509
nsim_dev_port_add_all+0x37/0xf0 drivers/net/netdevsim/dev.c:1570
nsim_drv_probe+0x8d6/0xc00 drivers/net/netdevsim/dev.c:1731
call_driver_probe drivers/base/dd.c:-1 [inline]
really_probe+0x254/0xae0 drivers/base/dd.c:706
__driver_probe_device+0x1e8/0x360 drivers/base/dd.c:868
page last free pid 5908 tgid 5908 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
__free_pages_prepare mm/page_alloc.c:1406 [inline]
__free_frozen_pages+0x10e7/0x11c0 mm/page_alloc.c:2950
__slab_free+0x252/0x2a0 mm/slub.c:5741
qlink_free mm/kasan/quarantine.c:163 [inline]
qlist_free_all+0x99/0x100 mm/kasan/quarantine.c:179
kasan_quarantine_reduce+0x148/0x160 mm/kasan/quarantine.c:286
__kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:350
kasan_slab_alloc include/linux/kasan.h:253 [inline]
slab_post_alloc_hook mm/slub.c:4584 [inline]
slab_alloc_node mm/slub.c:4917 [inline]
kmem_cache_alloc_noprof+0x355/0x650 mm/slub.c:4931
vm_area_alloc+0x24/0x140 mm/vma_init.c:32
__mmap_new_vma mm/vma.c:2547 [inline]
__mmap_region mm/vma.c:2774 [inline]
mmap_region+0x1263/0x2310 mm/vma.c:2860
do_mmap+0xc1e/0x10b0 mm/mmap.c:560
vm_mmap_pgoff+0x275/0x4e0 mm/util.c:581
ksys_mmap_pgoff+0x4a6/0x720 mm/mmap.c:606
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

Memory state around the buggy address:
ffff888039f51f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff888039f51f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888039f52000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff888039f52080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff888039f52100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
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