hfs: fix hfs_find_init() sb->ext_tree NULL ptr oops

Clement Lecigne reports a filesystem which causes a kernel oops in
hfs_find_init() trying to dereference sb->ext_tree which is NULL.

This proves to be because the filesystem has a corrupted MDB extent
record, where the extents file does not fit into the first three extents
in the file record (the first blocks).

In hfs_get_block() when looking up the blocks for the extent file
(HFS_EXT_CNID), it fails the first blocks special case, and falls
through to the extent code (which ultimately calls hfs_find_init())
which is in the process of being initialised.

Hfs avoids this scenario by always having the extents b-tree fitting
into the first blocks (the extents B-tree can't have overflow extents).

The fix is to check at mount time that the B-tree fits into first
blocks, i.e.  fail if HFS_I(inode)->alloc_blocks >=
HFS_I(inode)->first_blocks

Note, the existing commit 47f365eb57573 ("hfs: fix oops on mount with
corrupted btree extent records") becomes subsumed into this as a special
case, but only for the extents B-tree (HFS_EXT_CNID), it is perfectly
acceptable for the catalog B-Tree file to grow beyond three extents,
with the remaining extent descriptors in the extents overfow.

This fixes CVE-2011-2203

Reported-by: Clement LECIGNE <clement.lecigne@netasq.com>
Signed-off-by: Phillip Lougher <plougher@redhat.com>
Cc: Jeff Mahoney <jeffm@suse.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 15 insertions, 5 deletions

diff --git a/fs/hfs/btree.c b/fs/hfs/btree.c
index 3ebc437736fe..1cbdeea1db44 100644
--- a/fs/hfs/btree.c
+++ b/fs/hfs/btree.c
@@ -46,11 +46,26 @@ struct hfs_btree *hfs_btree_open(struct super_block *sb, u32 id, btree_keycmp ke
         case HFS_EXT_CNID:
                 hfs_inode_read_fork(tree->inode, mdb->drXTExtRec, mdb->drXTFlSize,
                                     mdb->drXTFlSize, be32_to_cpu(mdb->drXTClpSiz));
+                if (HFS_I(tree->inode)->alloc_blocks >
+                                        HFS_I(tree->inode)->first_blocks) {
+                        printk(KERN_ERR "hfs: invalid btree extent records\n");
+                        unlock_new_inode(tree->inode);
+                        goto free_inode;
+                }
+
                 tree->inode->i_mapping->a_ops = &hfs_btree_aops;
                 break;
         case HFS_CAT_CNID:
                 hfs_inode_read_fork(tree->inode, mdb->drCTExtRec, mdb->drCTFlSize,
                                     mdb->drCTFlSize, be32_to_cpu(mdb->drCTClpSiz));
+
+                if (!HFS_I(tree->inode)->first_blocks) {
+                        printk(KERN_ERR "hfs: invalid btree extent records "
+                                                                "(0 size).\n");
+                        unlock_new_inode(tree->inode);
+                        goto free_inode;
+                }
+
                 tree->inode->i_mapping->a_ops = &hfs_btree_aops;
                 break;
         default:
@@ -59,11 +74,6 @@ 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))