[PATCH v2 0/4] ocfs2: validate suballoc slot and bit of metadata blocks

[Joseph Qi]

The ocfs2 metadata validators trust the on-disk suballoc slot and bit
without checking them against the slot range of the mounted filesystem
and the capacity of the block group bitmap.  A corrupted image can
carry OCFS2_INVALID_SLOT or another out-of-range slot, or a suballoc
bit beyond the bitmap, and once the corresponding inode, extent block,
xattr block, dir index root or refcount block gets freed, the bad
value goes straight into ocfs2_get_system_file_inode() or
_ocfs2_free_suballoc_bits() and hits a BUG_ON() or runs off the end of
local_system_inodes[].

This series rejects such values at read time in the existing
validators, so a corrupted filesystem fails with -EROFS and remounts
read-only instead of crashing:

  patch 1 restricts dinodes with OCFS2_INVALID_SLOT to system inodes,
        completing fe7a283b3916 ("ocfs2: add suballoc slot check in
        ocfs2_validate_inode_block()"), and turns the "system file
        state is ambiguous" BUG_ON() in ocfs2_read_locked_inode() into
        an ocfs2_error();
  patch 2 rejects oversized suballoc bits in dinodes;
  patch 3 validates the suballoc slot and bit of xattr and dir index
        blocks;
  patch 4 validates the suballoc slot and bit of extent and refcount
        blocks.

The checks only enforce what the kernel and mkfs.ocfs2 already write:
a valid slot from meta_ac->ac_alloc_slot and a bit within the block
group bitmap, with system inodes carrying OCFS2_INVALID_SLOT plus
OCFS2_SYSTEM_FL and extent blocks using slot 0.  Nothing changes for
healthy filesystems.

Each new check was exercised under QEMU by corrupting the field in
question with an out-of-range value; with the series applied the
access fails with -EROFS and the filesystem remounts read-only instead
of hitting the BUG_ON().

Changes since v1:
  - Patch 1 also turns the system-file-state BUG_ON() in
    ocfs2_read_locked_inode() into ocfs2_error().  i_flags is on-disk
    data, so a crafted dinode with OCFS2_SYSTEM_FL passes the slot
    check and still hit that BUG() on a plain lookup.
  - Patches 2-4 now bound the suballoc bit against the block group
    bitmap capacity (block size minus the group descriptor header)
    instead of the raw block size, using a new
    ocfs2_suballoc_bits_per_block() helper.
  - Patch 3 also validates xb_suballoc_bit and dr_suballoc_bit.
  - Patch 4 also validates h_suballoc_bit, and adds rf_suballoc_slot
    and rf_suballoc_bit checks in ocfs2_validate_refcount_block().

Joseph Qi (4):
  ocfs2: restrict OCFS2_INVALID_SLOT suballoc slot to system inodes
  ocfs2: validate suballoc bit during inode read
  ocfs2: validate suballoc slot and bit of xattr and dir index blocks
  ocfs2: validate suballoc slot and bit of extent and refcount blocks

 fs/ocfs2/alloc.c        | 27 +++++++++++++++++++++
 fs/ocfs2/dir.c          | 27 +++++++++++++++++++++
 fs/ocfs2/inode.c        | 53 ++++++++++++++++++++++++++++++++++-------
 fs/ocfs2/ocfs2.h        | 11 +++++++++
 fs/ocfs2/refcounttree.c | 27 +++++++++++++++++++++
 fs/ocfs2/xattr.c        | 25 +++++++++++++++++++
 6 files changed, 161 insertions(+), 9 deletions(-)

-- 
2.39.3