hfs: fix oops on mount with corrupted btree extent records

A particular fsfuzzer run caused an hfs file system to crash on mount.
This is due to a corrupted MDB extent record causing a miscalculation of
HFS_I(inode)->first_blocks for the extent tree.  If the extent records are
zereod out, it won't trigger the first_blocks special case.  Instead it
falls through to the extent code which we're still in the middle of
initializing.

This patch catches the 0 size extent records, reports the corruption, and
fails the mount.

Reported-by: Ramon de Carvalho Valle <rcvalle@linux.vnet.ibm.com>
Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Cc: Valdis Kletnieks <Valdis.Kletnieks@vt.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 0 deletions

diff --git a/fs/hfs/btree.c b/fs/hfs/btree.c
index 9b9d6395bad3..052f214ea6f0 100644
--- a/fs/hfs/btree.c
+++ b/fs/hfs/btree.c
@@ -58,6 +58,11 @@ struct hfs_btree *hfs_btree_open(struct super_block *sb, u32 id, btree_keycmp ke
         }
         unlock_new_inode(tree->inode);
 
+        if (!HFS_I(tree->inode)->first_blocks) {
+                printk(KERN_ERR "hfs: invalid btree extent records (0 size).\n");
+                goto free_inode;
+        }
+
         mapping = tree->inode->i_mapping;
         page = read_mapping_page(mapping, 0, NULL);
         if (IS_ERR(page))