[v5.15] WARNING in inc_nlink

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 8020ae3c051d Linux 5.15.103
git tree: linux-5.15.y
console output: https://syzkaller.appspot.com/x/log.txt?x=156199bac80000
kernel config: https://syzkaller.appspot.com/x/.config?x=d4215fb4040f8f8d
dashboard link: https://syzkaller.appspot.com/bug?extid=642f43b47421d18b19dc
compiler: Debian clang version 15.0.7, GNU ld (GNU Binutils for Debian) 2.35.2

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/857e17de0f0a/disk-8020ae3c.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/9efc49fcd441/vmlinux-8020ae3c.xz
kernel image: https://storage.googleapis.com/syzbot-assets/f14c38b6bfa7/bzImage-8020ae3c.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+642f43...@syzkaller.appspotmail.com

------------[ cut here ]------------
WARNING: CPU: 1 PID: 10195 at fs/inode.c:364 inc_nlink+0x120/0x130
Modules linked in:
CPU: 1 PID: 10195 Comm: syz-executor.2 Not tainted 5.15.103-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/02/2023
RIP: 0010:inc_nlink+0x120/0x130 fs/inode.c:364
Code: ed ff e9 37 ff ff ff 44 89 e9 80 e1 07 80 c1 03 38 c1 0f 8c 49 ff ff ff 4c 89 ef e8 9a a2 ed ff e9 3c ff ff ff e8 30 19 a4 ff <0f> 0b eb 80 66 2e 0f 1f 84 00 00 00 00 00 66 90 41 57 41 56 53 48
RSP: 0018:ffffc900046b7b88 EFLAGS: 00010287
RAX: ffffffff81dc5fa0 RBX: 1ffff1100e6ba0e1 RCX: 0000000000040000
RDX: ffffc900060c1000 RSI: 000000000001fd10 RDI: 000000000001fd11
RBP: 0000000000000000 R08: ffffffff81dc5f1a R09: ffffed10033df258
R10: 0000000000000000 R11: dffffc0000000001 R12: dffffc0000000000
R13: ffff8880735d0708 R14: ffff8880735d06c0 R15: 0000000000000000
FS: 00007f54e9cdc700(0000) GS:ffff8880b9b00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020256000 CR3: 000000007942a000 CR4: 00000000003506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
fuse_link+0x370/0x5b0 fs/fuse/dir.c:939
vfs_link+0x65e/0x810 fs/namei.c:4486
do_linkat+0x5c8/0x9d0 fs/namei.c:4557
__do_sys_link fs/namei.c:4591 [inline]
__se_sys_link fs/namei.c:4589 [inline]
__x64_sys_link+0x82/0x90 fs/namei.c:4589
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x61/0xcb
RIP: 0033:0x7f54eb76a0f9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 f1 19 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 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f54e9cdc168 EFLAGS: 00000246 ORIG_RAX: 0000000000000056
RAX: ffffffffffffffda RBX: 00007f54eb889f80 RCX: 00007f54eb76a0f9
RDX: 0000000000000000 RSI: 0000000020000080 RDI: 0000000020000040
RBP: 00007f54eb7c5b39 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffde796baff R14: 00007f54e9cdc300 R15: 0000000000022000
</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.

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit: 8020ae3c051d Linux 5.15.103
git tree: linux-5.15.y

console output: https://syzkaller.appspot.com/x/log.txt?x=161d21d2c80000

kernel config: https://syzkaller.appspot.com/x/.config?x=d4215fb4040f8f8d
dashboard link: https://syzkaller.appspot.com/bug?extid=642f43b47421d18b19dc
compiler: Debian clang version 15.0.7, GNU ld (GNU Binutils for Debian) 2.35.2

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=139eb41cc80000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=134ac5bac80000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/857e17de0f0a/disk-8020ae3c.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/9efc49fcd441/vmlinux-8020ae3c.xz
kernel image: https://storage.googleapis.com/syzbot-assets/f14c38b6bfa7/bzImage-8020ae3c.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+642f43...@syzkaller.appspotmail.com

------------[ cut here ]------------

WARNING: CPU: 1 PID: 3585 at fs/inode.c:364 inc_nlink+0x120/0x130
Modules linked in:
CPU: 1 PID: 3585 Comm: syz-executor371 Not tainted 5.15.103-syzkaller #0

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/02/2023
RIP: 0010:inc_nlink+0x120/0x130 fs/inode.c:364
Code: ed ff e9 37 ff ff ff 44 89 e9 80 e1 07 80 c1 03 38 c1 0f 8c 49 ff ff ff 4c 89 ef e8 9a a2 ed ff e9 3c ff ff ff e8 30 19 a4 ff <0f> 0b eb 80 66 2e 0f 1f 84 00 00 00 00 00 66 90 41 57 41 56 53 48

RSP: 0018:ffffc90002c0fb88 EFLAGS: 00010293
RAX: ffffffff81dc5fa0 RBX: 1ffff1100e2b10e1 RCX: ffff88807e165700
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: ffffffff81dc5f1a R09: ffffed1029616158

R10: 0000000000000000 R11: dffffc0000000001 R12: dffffc0000000000

R13: ffff888071588708 R14: ffff8880715886c0 R15: 0000000000000000
FS: 00007f4386ead700(0000) GS:ffff8880b9b00000(0000) knlGS:0000000000000000

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

CR2: 00007f4386e8c718 CR3: 0000000019858000 CR4: 00000000003506e0

DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
fuse_link+0x370/0x5b0 fs/fuse/dir.c:939
vfs_link+0x65e/0x810 fs/namei.c:4486
do_linkat+0x5c8/0x9d0 fs/namei.c:4557
__do_sys_link fs/namei.c:4591 [inline]
__se_sys_link fs/namei.c:4589 [inline]
__x64_sys_link+0x82/0x90 fs/namei.c:4589
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x61/0xcb

RIP: 0033:0x7f4386efbb79
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 81 14 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 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f4386ead2f8 EFLAGS: 00000246 ORIG_RAX: 0000000000000056
RAX: ffffffffffffffda RBX: 00007f4386f8c4c0 RCX: 00007f4386efbb79
RDX: 00007f4386efbb79 RSI: 0000000020000080 RDI: 0000000020000040
RBP: 00007f4386f5a0e4 R08: 0000000000003065 R09: 0000000000000000
R10: 0000000000003065 R11: 0000000000000246 R12: 00007f4386f540d0
R13: 00007f4386f560d8 R14: 00007f4386f580e0 R15: 00007f4386f8c4c8
</TASK>

[syzbot]

syzbot suspects this issue could be fixed by backporting the following commit:

commit 97f044f690bac2b094bfb7fb2d177ef946c85880
git tree: upstream
Author: Miklos Szeredi <msze...@redhat.com>
Date: Fri Oct 22 15:03:02 2021 +0000

fuse: don't increment nlink in link()

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=170506d4e80000
kernel config: https://syzkaller.appspot.com/x/.config?x=ba8d5c9d6c5289f
dashboard link: https://syzkaller.appspot.com/bug?extid=642f43b47421d18b19dc
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=11c9fe4c280000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=10be25f2280000


Please keep in mind that other backports might be required as well.

For information about bisection process see: https://goo.gl/tpsmEJ#bisection