isofs: Fix out of bound access for corrupted isofs image

When isofs image is suitably corrupted isofs_read_inode() can read data
beyond the end of buffer. Sanity-check the directory entry length before
using it.

Reported-and-tested-by: syzbot+6fc7fb214625d82af7d1@syzkaller.appspotmail.com
CC: stable@vger.kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>

fs/isofs/inode.c

@@ -1322,6 +1322,8 @@ static int isofs_read_inode(struct inode *inode, int relocated)
 
 	de = (struct iso_directory_record *) (bh->b_data + offset);
 	de_len = *(unsigned char *) de;
+	if (de_len < sizeof(struct iso_directory_record))
+		goto fail;
 
 	if (offset + de_len > bufsize) {
 		int frag1 = bufsize - offset;