Squashfs: add sanity checks to xattr reading at mount time

These checks add sanity checking of the mount-time xattr structures.
Signed-off-by: Phillip Lougher <phillip@lougher.demon.co.uk>

fs/squashfs/xattr_id.c

@@ -76,6 +76,17 @@ __le64 *squashfs_read_xattr_id_table(struct super_block *sb, u64 start,
 	*xattr_table_start = le64_to_cpu(id_table->xattr_table_start);
 	*xattr_ids = le32_to_cpu(id_table->xattr_ids);
 	kfree(id_table);
+
+	/* Sanity check values */
+
+	/* there is always at least one xattr id */
+	if (*xattr_ids == 0)
+		return ERR_PTR(-EINVAL);
+
+	/* xattr_table should be less than start */
+	if (*xattr_table_start >= start)
+		return ERR_PTR(-EINVAL);
+
 	len = SQUASHFS_XATTR_BLOCK_BYTES(*xattr_ids);
 
 	TRACE("In read_xattr_index_table, length %d\n", len);