[PATCH] isofs: Fix handling of directories with tight blocks

[Jan Kara <jack@suse.cz>]

Thomas has reported that after commit b2eb2e288604 ("isofs: Drop support
of directory entries straddling blocks") some isofs images of Fedora
miss some entries in some directories. The problem is triggered when
directory entries are packed in a block in such a way that they exactly
fit the block (which BTW mkisofs doesn't do so I didn't catch this bug
when testing with my images). Fix readdir and lookup code to properly
transition to the next block when directory block is tightly packed.

Link: https://bugzilla.redhat.com/show_bug.cgi?id=2535353
Reported-by: Thomas Schmitt <scdbackup@gmx.net>
Reported-by: Matthias Goergens <matthias.goergens@gmail.com>
Fixes: b2eb2e288604 ("isofs: Drop support of directory entries straddling blocks")
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/isofs/dir.c   | 18 +++++++-----------
 fs/isofs/namei.c | 14 ++++++++------
 2 files changed, 15 insertions(+), 17 deletions(-)

I plan to push this fix to Linus at the end of the week.

diff --git a/fs/isofs/dir.c b/fs/isofs/dir.c
index c7ca7603e97a..5e541e765f54 100644
--- a/fs/isofs/dir.c
+++ b/fs/isofs/dir.c
@@ -110,25 +110,21 @@ static int do_isofs_readdir(struct inode *inode, struct file *file,
 				return 0;
 		}
 
-		de = (struct iso_directory_record *) (bh->b_data + offset);
-
-		de_len = *(unsigned char *)de;
-
+		de = (struct iso_directory_record *)(bh->b_data + offset);
 		/*
-		 * If the length byte is zero, we should move on to the next
-		 * CDROM sector.  If we are at the end of the directory, we
-		 * kick out of the while loop.
+		 * If we are at the end of a block (or at its zero-padded
+		 * tail), move on to the next CDROM sector.  If we are at the
+		 * end of the directory, we'll abort the while loop.
 		 */
-
-		if (de_len == 0) {
+		if (offset >= bufsize || de->length[0] == 0) {
 			brelse(bh);
 			bh = NULL;
-			ctx->pos = (ctx->pos + ISOFS_BLOCK_SIZE) & ~(ISOFS_BLOCK_SIZE - 1);
+			ctx->pos = round_up(ctx->pos, bufsize);
 			block = ctx->pos >> bufbits;
 			offset = 0;
 			continue;
 		}
-
+		de_len = de->length[0];
 		block_saved = block;
 		offset_saved = offset;
 		offset += de_len;
diff --git a/fs/isofs/namei.c b/fs/isofs/namei.c
index 010682f5901a..e7efeea16451 100644
--- a/fs/isofs/namei.c
+++ b/fs/isofs/namei.c
@@ -74,18 +74,20 @@ isofs_find_entry(struct inode *dir, struct dentry *dentry,
 				return 0;
 		}
 
-		de = (struct iso_directory_record *) (bh->b_data + offset);
-
-		de_len = *(unsigned char *) de;
-		if (!de_len) {
+		de = (struct iso_directory_record *)(bh->b_data + offset);
+		/*
+		 * If we are at the end of the block or at its zero-padded
+		 * length, move to the next block.
+		 */
+		if (offset >= bufsize || de->length[0] == 0) {
 			brelse(bh);
 			bh = NULL;
-			f_pos = (f_pos + ISOFS_BLOCK_SIZE) & ~(ISOFS_BLOCK_SIZE - 1);
+			f_pos = round_up(f_pos, bufsize);
 			block = f_pos >> bufbits;
 			offset = 0;
 			continue;
 		}
-
+		de_len = de->length[0];
 		block_saved = bh->b_blocknr;
 		offset_saved = offset;
 		offset += de_len;
-- 
2.51.0