[v5.15] WARNING: refcount bug in config_item_get

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 674f684f7c61 Linux 5.15.212
git tree: linux-5.15.y
console output: https://syzkaller.appspot.com/x/log.txt?x=13ff86b9580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f161cbc9aef65db0
dashboard link: https://syzkaller.appspot.com/bug?extid=a1bee4f9304714f38047
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=105f2499580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=17f866b9580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/f55be2937b89/disk-674f684f.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/a19fb0ffc049/vmlinux-674f684f.xz
kernel image: https://storage.googleapis.com/syzbot-assets/365d4529a007/bzImage-674f684f.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+a1bee4...@syzkaller.appspotmail.com

------------[ cut here ]------------
refcount_t: addition on 0; use-after-free.
WARNING: CPU: 1 PID: 5440 at lib/refcount.c:25 refcount_warn_saturate+0xff/0x1a0 lib/refcount.c:25
Modules linked in:
CPU: 1 PID: 5440 Comm: syz.2.1074 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
RIP: 0010:refcount_warn_saturate+0xff/0x1a0 lib/refcount.c:25
Code: 09 01 48 c7 c7 20 04 7a 8a e8 bd ba cc 05 0f 0b eb e0 e8 64 92 90 fd c6 05 7f e5 8e 09 01 48 c7 c7 60 03 7a 8a e8 a1 ba cc 05 <0f> 0b eb c4 e8 48 92 90 fd c6 05 64 e5 8e 09 01 48 c7 c7 c0 03 7a
RSP: 0018:ffffc90005e37c68 EFLAGS: 00010246
RAX: 798530d8ee696600 RBX: 0000000000000002 RCX: ffff8880283b8000
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
RBP: 0000000000000000 R08: ffffc90005e37787 R09: 1ffff92000bc6ef0
R10: dffffc0000000000 R11: fffff52000bc6ef1 R12: ffff88807a1ad4b0
R13: dffffc0000000000 R14: 0000000000000002 R15: ffff88807801d000
FS: 0000555588b23500(0000) GS:ffff8880b9100000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055555698da38 CR3: 000000005ca8f000 CR4: 00000000003506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
__refcount_add include/linux/refcount.h:-1 [inline]
__refcount_inc include/linux/refcount.h:250 [inline]
refcount_inc include/linux/refcount.h:267 [inline]
kref_get include/linux/kref.h:45 [inline]
config_item_get+0x7f/0x90 fs/configfs/item.c:104
configfs_get_config_item fs/configfs/configfs_internal.h:128 [inline]
get_target fs/configfs/symlink.c:125 [inline]
configfs_symlink+0x463/0x13b0 fs/configfs/symlink.c:191
vfs_symlink+0x245/0x3d0 fs/namei.c:4437
do_symlinkat+0x1ab/0x6b0 fs/namei.c:4466
__do_sys_symlinkat fs/namei.c:4483 [inline]
__se_sys_symlinkat fs/namei.c:4480 [inline]
__x64_sys_symlinkat+0x95/0xa0 fs/namei.c:4480
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7faeaca69e99
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:00007ffe812208a8 EFLAGS: 00000246 ORIG_RAX: 000000000000010a
RAX: ffffffffffffffda RBX: 00007faeaccf1fa0 RCX: 00007faeaca69e99
RDX: 0000200000000340 RSI: ffffffffffffff9c RDI: 0000200000000300
RBP: 00007faeacaffeaf R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007faeaccf1fac R14: 00007faeaccf1fa0 R15: 00007faeaccf1fa0
</TASK>


---
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[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: dc5c83b7f5f8 Linux 6.1.178
git tree: linux-6.1.y
console output: https://syzkaller.appspot.com/x/log.txt?x=151451b9580000
kernel config: https://syzkaller.appspot.com/x/.config?x=31dfefc4a14efea3
dashboard link: https://syzkaller.appspot.com/bug?extid=fc32b6c2798db135badf

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/a9aa438e39c2/disk-dc5c83b7.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/a7b5afd2e170/vmlinux-dc5c83b7.xz
kernel image: https://storage.googleapis.com/syzbot-assets/3c7673d370fb/bzImage-dc5c83b7.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:

Reported-by: syzbot+fc32b6...@syzkaller.appspotmail.com

------------[ cut here ]------------
refcount_t: addition on 0; use-after-free.

WARNING: CPU: 0 PID: 5666 at lib/refcount.c:25 refcount_warn_saturate+0xff/0x1a0 lib/refcount.c:25
Modules linked in:
CPU: 0 PID: 5666 Comm: syz.3.417 Not tainted syzkaller #0

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
RIP: 0010:refcount_warn_saturate+0xff/0x1a0 lib/refcount.c:25

Code: 09 01 48 c7 c7 40 1b df 8a e8 7d f5 37 fd 0f 0b eb e0 e8 f4 70 6c fd c6 05 b5 dd f6 09 01 48 c7 c7 80 1a df 8a e8 61 f5 37 fd <0f> 0b eb c4 e8 d8 70 6c fd c6 05 9a dd f6 09 01 48 c7 c7 e0 1a df
RSP: 0018:ffffc90003f37c68 EFLAGS: 00010246
RAX: 9cb5e2555ecec600 RBX: 0000000000000002 RCX: 0000000000080000
RDX: ffffc9000fb2d000 RSI: 000000000000556a RDI: 000000000000556b
RBP: 0000000000000000 R08: ffffc90003f378e7 R09: 1ffff920007e6f1c
R10: dffffc0000000000 R11: fffff520007e6f1d R12: ffff8881482fefb0
R13: dffffc0000000000 R14: 0000000000000002 R15: ffff888076d25800
FS: 00007fb3461826c0(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: 00007fb346181ff8 CR3: 000000002ea41000 CR4: 00000000003506f0

DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
__refcount_add include/linux/refcount.h:-1 [inline]
__refcount_inc include/linux/refcount.h:250 [inline]
refcount_inc include/linux/refcount.h:267 [inline]
kref_get include/linux/kref.h:45 [inline]
config_item_get+0x7f/0x90 fs/configfs/item.c:104
configfs_get_config_item fs/configfs/configfs_internal.h:128 [inline]
get_target fs/configfs/symlink.c:125 [inline]

configfs_symlink+0x463/0x13c0 fs/configfs/symlink.c:191
vfs_symlink+0x245/0x3d0 fs/namei.c:4479
do_symlinkat+0x1b6/0x400 fs/namei.c:4508
__do_sys_symlinkat fs/namei.c:4525 [inline]
__se_sys_symlinkat fs/namei.c:4522 [inline]
__x64_sys_symlinkat+0x95/0xa0 fs/namei.c:4522
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: 0033:0x7fb34539de99

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:00007fb346182028 EFLAGS: 00000246 ORIG_RAX: 000000000000010a
RAX: ffffffffffffffda RBX: 00007fb345626090 RCX: 00007fb34539de99
RDX: 0000200000000200 RSI: ffffffffffffff9c RDI: 00002000000001c0
RBP: 00007fb345433eaf R08: 0000000000000000 R09: 0000000000000000

R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000

R13: 00007fb345626128 R14: 00007fb345626090 R15: 00007ffc54ba61d8

</TASK>


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title