udf: New directory iteration code

Add new support code for iterating directory entries. The code is also
more carefully verifying validity of on-disk directory entries to avoid
crashes on malicious media.
Signed-off-by: Jan Kara <jack@suse.cz>

fs/udf/udfdecl.h

@@ -86,6 +86,24 @@ extern const struct address_space_operations udf_aops;
 extern const struct address_space_operations udf_adinicb_aops;
 extern const struct address_space_operations udf_symlink_aops;
 
+struct udf_fileident_iter {
+	struct inode *dir;		/* Directory we are working with */
+	loff_t pos;			/* Logical position in a dir */
+	struct buffer_head *bh[2];	/* Buffer containing 'pos' and possibly
+					 * next buffer if entry straddles
+					 * blocks */
+	struct kernel_lb_addr eloc;	/* Start of extent containing 'pos' */
+	uint32_t elen;			/* Length of extent containing 'pos' */
+	sector_t loffset;		/* Block offset of 'pos' within above
+					 * extent */
+	struct extent_position epos;	/* Position after the above extent */
+	struct fileIdentDesc fi;	/* Copied directory entry */
+	uint8_t *name;			/* Pointer to entry name */
+	uint8_t namebuf[UDF_NAME_LEN_CS0]; /* Storage for entry name in case
+					 * the name is split between two blocks
+					 */
+};
+
 struct udf_fileident_bh {
 	struct buffer_head *sbh;
 	struct buffer_head *ebh;
@@ -243,6 +261,11 @@ extern udf_pblk_t udf_new_block(struct super_block *sb, struct inode *inode,
 				 uint16_t partition, uint32_t goal, int *err);
 
 /* directory.c */
+int udf_fiiter_init(struct udf_fileident_iter *iter, struct inode *dir,
+		    loff_t pos);
+int udf_fiiter_advance(struct udf_fileident_iter *iter);
+void udf_fiiter_release(struct udf_fileident_iter *iter);
+void udf_fiiter_write_fi(struct udf_fileident_iter *iter, uint8_t *impuse);
 extern struct fileIdentDesc *udf_fileident_read(struct inode *, loff_t *,
 						struct udf_fileident_bh *,
 						struct fileIdentDesc *,