ext2: skip pages past number of blocks in ext2_find_entry (CVE-2006-6054)

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: Adrian Bunk <bunk@stusta.de>

diff --git a/fs/ext2/dir.c b/fs/ext2/dir.c
index b3dbd716cd3a19b537c87b88048cd54ee43d7e50..8a27dcc096b56148fe4a5c2192cfbf7c54af3268 100644 (file)
--- a/fs/ext2/dir.c
+++ b/fs/ext2/dir.c
@@ -369,6 +369,14 @@ 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;