[PATCH] ext2: skip pages past number of blocks in ext2_find_entry

This one was pointed out on the MOKB site:
http://kernelfun.blogspot.com/2006/11/mokb-09-11-2006-linux-26x-ext2checkpage.html

If a directory's i_size is corrupted, ext2_find_entry() will keep
processing pages until the i_size is reached, even if there are no more
blocks associated with the directory inode.  This patch puts in some
minimal sanity-checking so that we don't keep checking pages (and issuing
errors) if we know there can be no more data to read, based on the block
count of the directory inode.

This is somewhat similar in approach to the ext3 patch I sent earlier this
year.
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/ext2/dir.c

@@ -368,6 +368,14 @@ struct ext2_dir_entry_2 * ext2_find_entry (struct inode * dir,
 		}
 		if (++n >= npages)
 			n = 0;
+		/* next page is past the blocks we've got */
+		if (unlikely(n > (dir->i_blocks >> (PAGE_CACHE_SHIFT - 9)))) {
+			ext2_error(dir->i_sb, __FUNCTION__,
+				"dir %lu size %lld exceeds block count %llu",
+				dir->i_ino, dir->i_size,
+				(unsigned long long)dir->i_blocks);
+			goto out;
+		}
 	} while (n != start);
 out:
 	return NULL;