f2fs: prevent kernel warning due to negative i_nlink from corrupted image

BugLink: https://bugs.launchpad.net/bugs/2120812

commit 42cb74a92adaf88061039601ddf7c874f58b554e upstream.

WARNING: CPU: 1 PID: 9426 at fs/inode.c:417 drop_nlink+0xac/0xd0
home/cc/linux/fs/inode.c:417
Modules linked in:
CPU: 1 UID: 0 PID: 9426 Comm: syz-executor568 Not tainted
6.14.0-12627-g94d471a4f428 #2 PREEMPT(full)
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
1.13.0-1ubuntu1.1 04/01/2014
RIP: 0010:drop_nlink+0xac/0xd0 home/cc/linux/fs/inode.c:417
Code: 48 8b 5d 28 be 08 00 00 00 48 8d bb 70 07 00 00 e8 f9 67 e6 ff
f0 48 ff 83 70 07 00 00 5b 5d e9 9a 12 82 ff e8 95 12 82 ff 90
<0f> 0b 90 c7 45 48 ff ff ff ff 5b 5d e9 83 12 82 ff e8 fe 5f e6
ff
RSP: 0018:ffffc900026b7c28 EFLAGS: 00010293
RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff8239710f
RDX: ffff888041345a00 RSI: ffffffff8239717b RDI: 0000000000000005
RBP: ffff888054509ad0 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000000000 R11: ffffffff9ab36f08 R12: ffff88804bb40000
R13: ffff8880545091e0 R14: 0000000000008000 R15: ffff8880545091e0
FS:  000055555d0c5880(0000) GS:ffff8880eb3e3000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f915c55b178 CR3: 0000000050d20000 CR4: 0000000000352ef0
Call Trace:
 <task>
 f2fs_i_links_write home/cc/linux/fs/f2fs/f2fs.h:3194 [inline]
 f2fs_drop_nlink+0xd1/0x3c0 home/cc/linux/fs/f2fs/dir.c:845
 f2fs_delete_entry+0x542/0x1450 home/cc/linux/fs/f2fs/dir.c:909
 f2fs_unlink+0x45c/0x890 home/cc/linux/fs/f2fs/namei.c:581
 vfs_unlink+0x2fb/0x9b0 home/cc/linux/fs/namei.c:4544
 do_unlinkat+0x4c5/0x6a0 home/cc/linux/fs/namei.c:4608
 __do_sys_unlink home/cc/linux/fs/namei.c:4654 [inline]
 __se_sys_unlink home/cc/linux/fs/namei.c:4652 [inline]
 __x64_sys_unlink+0xc5/0x110 home/cc/linux/fs/namei.c:4652
 do_syscall_x64 home/cc/linux/arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xc7/0x250 home/cc/linux/arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fb3d092324b
Code: 73 01 c3 48 c7 c1 c0 ff ff ff f7 d8 64 89 01 48 83 c8 ff c3 66
2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa b8 57 00 00 00 0f 05
&lt;48&gt; 3d 01 f0 ff ff 73 01 c3 48 c7 c1 c0 ff ff ff f7 d8 64 89 01
48
RSP: 002b:00007ffdc232d938 EFLAGS: 00000206 ORIG_RAX: 0000000000000057
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fb3d092324b
RDX: 00007ffdc232d960 RSI: 00007ffdc232d960 RDI: 00007ffdc232d9f0
RBP: 00007ffdc232d9f0 R08: 0000000000000001 R09: 00007ffdc232d7c0
R10: 00000000fffffffd R11: 0000000000000206 R12: 00007ffdc232eaf0
R13: 000055555d0cebb0 R14: 00007ffdc232d958 R15: 0000000000000001
 </task>

Cc: stable@vger.kernel.org
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Noah Wager <noah.wager@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

Author: Jaegeuk Kim

fs/f2fs/namei.c

@@ -569,6 +569,15 @@ static int f2fs_unlink(struct inode *dir, struct dentry *dentry)
 		goto fail;
 	}
 
+	if (unlikely(inode->i_nlink == 0)) {
+		f2fs_warn(F2FS_I_SB(inode), "%s: inode (ino=%lx) has zero i_nlink",
+			  __func__, inode->i_ino);
+		err = -EFSCORRUPTED;
+		set_sbi_flag(F2FS_I_SB(inode), SBI_NEED_FSCK);
+		f2fs_put_page(page, 0);
+		goto fail;
+	}
+
 	f2fs_balance_fs(sbi, true);
 
 	f2fs_lock_op(sbi);