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

[Phillip Lougher]

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 47f365eb575735c6b2edf5d08e0d16d26a9c23bd
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...@netasq.com>
Signed-off-by: Phillip Lougher <plou...@redhat.com>
---
fs/hfs/btree.c | 20 +++++++++++++++-----
1 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/fs/hfs/btree.c b/fs/hfs/btree.c
index 3ebc437..c28b7fa 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))
--
1.7.1

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[Phillip Lougher]

(Re-send due to missing off [PATCH] in the subject line)