[moderation] [i2c?] WARNING: refcount bug in i2c_get_adapter

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 211ddde0823f Linux 6.18-rc2
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=156b4d42580000
kernel config: https://syzkaller.appspot.com/x/.config?x=216353986aa62c5d
dashboard link: https://syzkaller.appspot.com/bug?extid=310912aee5438db9d3b8
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
CC: [linu...@vger.kernel.org linux-...@vger.kernel.org wsa+r...@sang-engineering.com]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/07371cf02d4e/disk-211ddde0.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/27220c94ca08/vmlinux-211ddde0.xz
kernel image: https://storage.googleapis.com/syzbot-assets/12abd01b8291/bzImage-211ddde0.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+310912...@syzkaller.appspotmail.com

------------[ cut here ]------------
refcount_t: addition on 0; use-after-free.
WARNING: CPU: 1 PID: 6572 at lib/refcount.c:25 refcount_warn_saturate+0xfa/0x1d0 lib/refcount.c:25
Modules linked in:
CPU: 1 UID: 0 PID: 6572 Comm: syz.2.237 Not tainted syzkaller #0 PREEMPT_{RT,(full)}
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
RIP: 0010:refcount_warn_saturate+0xfa/0x1d0 lib/refcount.c:25
Code: 00 00 e8 e9 f5 3d fd 5b 41 5e c3 cc cc cc cc cc e8 db f5 3d fd c6 05 b8 91 60 0a 01 90 48 c7 c7 a0 9a 3e 8b e8 e7 3d 02 fd 90 <0f> 0b 90 90 eb d7 e8 bb f5 3d fd c6 05 99 91 60 0a 01 90 48 c7 c7
RSP: 0018:ffffc9000cdef6d8 EFLAGS: 00010246
RAX: 07f404c01321b500 RBX: 0000000000000002 RCX: 0000000000080000
RDX: ffffc90005d09000 RSI: 00000000000008d8 RDI: 00000000000008d9
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: dffffc0000000000 R11: ffffed101712487b R12: ffffffff8b995c88
R13: dffffc0000000000 R14: ffff88805dd48390 R15: dffffc0000000000
FS: 00007fd67c35e6c0(0000) GS:ffff888126cc2000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b3001eff8 CR3: 000000003a534000 CR4: 00000000003526f0
Call Trace:
<TASK>
__refcount_add include/linux/refcount.h:-1 [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]
kobject_get+0xfd/0x120 lib/kobject.c:643
i2c_get_adapter+0x6d/0xa0 drivers/i2c/i2c-core-base.c:2612
i2cdev_open+0x48/0x190 drivers/i2c/i2c-dev.c:604
chrdev_open+0x4cf/0x5e0 fs/char_dev.c:414
do_dentry_open+0x9b1/0x1350 fs/open.c:965
vfs_open+0x3b/0x350 fs/open.c:1097
do_open fs/namei.c:3975 [inline]
path_openat+0x2ef1/0x3840 fs/namei.c:4134
do_filp_open+0x1fa/0x410 fs/namei.c:4161
do_sys_openat2+0x121/0x1c0 fs/open.c:1437
do_sys_open fs/open.c:1452 [inline]
__do_sys_openat fs/open.c:1468 [inline]
__se_sys_openat fs/open.c:1463 [inline]
__x64_sys_openat+0x138/0x170 fs/open.c:1463
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fd67e0fd810
Code: 48 89 44 24 20 75 93 44 89 54 24 0c e8 69 95 02 00 44 8b 54 24 0c 89 da 48 89 ee 41 89 c0 bf 9c ff ff ff b8 01 01 00 00 0f 05 <48> 3d 00 f0 ff ff 77 38 44 89 c7 89 44 24 0c e8 bc 95 02 00 8b 44
RSP: 002b:00007fd67c35db70 EFLAGS: 00000293 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 0000000000002603 RCX: 00007fd67e0fd810
RDX: 0000000000002603 RSI: 00007fd67c35dc10 RDI: 00000000ffffff9c
RBP: 00007fd67c35dc10 R08: 0000000000000000 R09: 00232d6332692f76
R10: 0000000000000000 R11: 0000000000000293 R12: cccccccccccccccd
R13: 00007fd67e356038 R14: 00007fd67e355fa0 R15: 00007ffec547dee8
</TASK>


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