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 >=
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 <firstname.lastname@example.org>
Signed-off-by: Phillip Lougher <email@example.com>
Cc: Jeff Mahoney <firstname.lastname@example.org>
Cc: Christoph Hellwig <email@example.com>
Signed-off-by: Andrew Morton <firstname.lastname@example.org>
Signed-off-by: Linus Torvalds <email@example.com>