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

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
KASAN: slab-use-after-free Write in config_item_get

==================================================================
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 ffff88804491f01c by task syz.1.545/7868

CPU: 1 UID: 0 PID: 7868 Comm: syz.1.545 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/08/2026
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
 get_target fs/configfs/symlink.c:139 [inline]
 configfs_symlink+0x407/0x11d0 fs/configfs/symlink.c:200
 vfs_symlink+0x18b/0x330 fs/namei.c:5794
 filename_symlinkat+0x1cd/0x420 fs/namei.c:5819
 __do_sys_symlinkat fs/namei.c:5839 [inline]
 __se_sys_symlinkat+0x4e/0x2b0 fs/namei.c:5834
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84


Tested on:

commit:         a7c1290e configfs: pin the symlink target's dirent ins..
git tree:       https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=1626c115580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=6d794b10c2a1184e
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

Note: no patches were applied.