udf: Preserve link count of system files

System files in UDF filesystem have link count 0. To not confuse VFS we
fudge the link count to be 1 when reading such inodes however we forget
to restore the link count of 0 when writing such inodes. Fix that.

CC: stable@vger.kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>

fs/udf/inode.c

@@ -1301,6 +1301,7 @@ static int udf_read_inode(struct inode *inode, bool hidden_inode)
 		ret = -EIO;
 		goto out;
 	}
+	iinfo->i_hidden = hidden_inode;
 	iinfo->i_unique = 0;
 	iinfo->i_lenEAttr = 0;
 	iinfo->i_lenExtents = 0;
@@ -1636,8 +1637,12 @@ static int udf_update_inode(struct inode *inode, int do_sync)
 
 	if (S_ISDIR(inode->i_mode) && inode->i_nlink > 0)
 		fe->fileLinkCount = cpu_to_le16(inode->i_nlink - 1);
-	else
-		fe->fileLinkCount = cpu_to_le16(inode->i_nlink);
+	else {
+		if (iinfo->i_hidden)
+			fe->fileLinkCount = cpu_to_le16(0);
+		else
+			fe->fileLinkCount = cpu_to_le16(inode->i_nlink);
+	}
 
 	fe->informationLength = cpu_to_le64(inode->i_size);
 

fs/udf/super.c

@@ -147,6 +147,7 @@ static struct inode *udf_alloc_inode(struct super_block *sb)
 	ei->i_next_alloc_goal = 0;
 	ei->i_strat4096 = 0;
 	ei->i_streamdir = 0;
+	ei->i_hidden = 0;
 	init_rwsem(&ei->i_data_sem);
 	ei->cached_extent.lstart = -1;
 	spin_lock_init(&ei->i_extent_cache_lock);

fs/udf/udf_i.h

@@ -44,7 +44,8 @@ struct udf_inode_info {
 	unsigned		i_use : 1;	/* unallocSpaceEntry */
 	unsigned		i_strat4096 : 1;
 	unsigned		i_streamdir : 1;
-	unsigned		reserved : 25;
+	unsigned		i_hidden : 1;	/* hidden system inode */
+	unsigned		reserved : 24;
 	__u8			*i_data;
 	struct kernel_lb_addr	i_locStreamdir;
 	__u64			i_lenStreams;