udf: Don't modify filesystem for read-only mounts

When read-write mount of a filesystem is requested but we find out we
can mount the filesystem only in read-only mode, we still modify
LVID in udf_close_lvid(). That is both unnecessary and contrary to
expectation that when we fall back to read-only mount we don't modify
the filesystem.

Make sure we call udf_close_lvid() only if we called udf_open_lvid() so
that filesystem gets modified only if we verified we are allowed to
write to it.
Reported-by: Karel Zak <kzak@redhat.com>
Signed-off-by: Jan Kara <jack@suse.com>

fs/udf/super.c

@@ -2070,6 +2070,7 @@ static int udf_fill_super(struct super_block *sb, void *options, int silent)
 	struct udf_options uopt;
 	struct kernel_lb_addr rootdir, fileset;
 	struct udf_sb_info *sbi;
+	bool lvid_open = false;
 
 	uopt.flags = (1 << UDF_FLAG_USE_AD_IN_ICB) | (1 << UDF_FLAG_STRICT);
 	uopt.uid = INVALID_UID;
@@ -2216,8 +2217,10 @@ static int udf_fill_super(struct super_block *sb, void *options, int silent)
 			 le16_to_cpu(ts.year), ts.month, ts.day,
 			 ts.hour, ts.minute, le16_to_cpu(ts.typeAndTimezone));
 	}
-	if (!(sb->s_flags & MS_RDONLY))
+	if (!(sb->s_flags & MS_RDONLY)) {
 		udf_open_lvid(sb);
+		lvid_open = true;
+	}
 
 	/* Assign the root inode */
 	/* assign inodes by physical block number */
@@ -2248,7 +2251,7 @@ static int udf_fill_super(struct super_block *sb, void *options, int silent)
 	if (UDF_QUERY_FLAG(sb, UDF_FLAG_NLS_MAP))
 		unload_nls(sbi->s_nls_map);
 #endif
-	if (!(sb->s_flags & MS_RDONLY))
+	if (lvid_open)
 		udf_close_lvid(sb);
 	brelse(sbi->s_lvid_bh);
 	udf_sb_free_partitions(sb);