[moderation] [v9fs?] WARNING: refcount bug in v9fs_fid_find (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 317c7bc0ef03 Merge tag 'mmc-v6.9-rc1' of git://git.kernel...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14262ab5180000
kernel config: https://syzkaller.appspot.com/x/.config?x=f64ec427e98bccd7
dashboard link: https://syzkaller.appspot.com/bug?extid=8bab945580aa1a81c9b3
compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
CC: [asma...@codewreck.org eri...@kernel.org linux-...@vger.kernel.org linux-...@vger.kernel.org linu...@crudebyte.com lu...@ionkov.net v9...@lists.linux.dev]

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

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7bc7510fe41f/non_bootable_disk-317c7bc0.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/efab473d72c0/vmlinux-317c7bc0.xz
kernel image: https://storage.googleapis.com/syzbot-assets/5ba3f56d362d/bzImage-317c7bc0.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+8bab94...@syzkaller.appspotmail.com

------------[ cut here ]------------
refcount_t: addition on 0; use-after-free.
WARNING: CPU: 3 PID: 7116 at lib/refcount.c:25 refcount_warn_saturate+0x1ca/0x210 lib/refcount.c:25
Modules linked in:
CPU: 3 PID: 7116 Comm: syz-executor.1 Not tainted 6.9.0-rc1-syzkaller-00178-g317c7bc0ef03 #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
RIP: 0010:refcount_warn_saturate+0x1ca/0x210 lib/refcount.c:25
Code: ff 89 de e8 78 c1 0f fd 84 db 0f 85 e6 fe ff ff e8 eb c6 0f fd c6 05 1f f1 4c 0b 01 90 48 c7 c7 c0 e4 8e 8b e8 d7 34 d2 fc 90 <0f> 0b 90 90 e9 c3 fe ff ff e8 c8 c6 0f fd c6 05 fa f0 4c 0b 01 90
RSP: 0018:ffffc90003c9f888 EFLAGS: 00010286
RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffc900062bc000
RDX: 0000000000040000 RSI: ffffffff814fe156 RDI: 0000000000000001
RBP: ffff88802381630c R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000001 R12: ffff88802381630c
R13: dffffc0000000000 R14: 1ffff92000793f15 R15: 0000000000000000
FS: 00007f2618b566c0(0000) GS:ffff88806b300000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fb08f5ad988 CR3: 0000000025288000 CR4: 0000000000350ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
__refcount_add include/linux/refcount.h:190 [inline]
__refcount_inc include/linux/refcount.h:241 [inline]
refcount_inc include/linux/refcount.h:258 [inline]
p9_fid_get include/net/9p/client.h:262 [inline]
v9fs_fid_find+0x2e2/0x330 fs/9p/fid.c:129
v9fs_fid_lookup_with_uid fs/9p/fid.c:181 [inline]
v9fs_fid_lookup+0xd8/0xf20 fs/9p/fid.c:314
v9fs_fid_clone fs/9p/fid.h:29 [inline]
v9fs_file_open+0x5f0/0xba0 fs/9p/vfs_file.c:56
do_dentry_open+0x8da/0x18c0 fs/open.c:955
do_open fs/namei.c:3642 [inline]
path_openat+0x1dfb/0x2990 fs/namei.c:3799
do_filp_open+0x1dc/0x430 fs/namei.c:3826
do_sys_openat2+0x17a/0x1e0 fs/open.c:1406
do_sys_open fs/open.c:1421 [inline]
__do_sys_open fs/open.c:1429 [inline]
__se_sys_open fs/open.c:1425 [inline]
__x64_sys_open+0x154/0x1e0 fs/open.c:1425
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xd2/0x260 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x6d/0x75
RIP: 0033:0x7f2617e7dda9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 e1 20 00 00 90 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 b0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f2618b560c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000002
RAX: ffffffffffffffda RBX: 00007f2617fac050 RCX: 00007f2617e7dda9
RDX: 00000000000000a0 RSI: 0000000000000001 RDI: 0000000020000180
RBP: 00007f2617eca47a R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 000000000000006e R14: 00007f2617fac050 R15: 00007ffe6ac87e18
</TASK>


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