Re: [PATCH] xfs: AGI length should be bounds checked

[Dave Chinner <david@fromorbit.com>]

On Sun, Jul 02, 2023 at 09:25:55AM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <djwong@kernel.org>
> 
> Similar to the recent patch strengthening the AGF agf_length
> verification, the AGI verifier does not check that the AGI length field
> is within known good bounds.  This isn't currently checked by runtime
> kernel code, yet we assume in many places that it is correct and verify
> other metadata against it.
> 
> Add length verification to the AGI verifier.  Just like the AGF length
> checking, the length of the AGI must be equal to the size of the AG
> specified in the superblock, unless it is the last AG in the filesystem.
> In that case, it must be less than or equal to sb->sb_agblocks and
> greater than XFS_MIN_AG_BLOCKS, which is the smallest AG a growfs
> operation will allow to exist.
> 
> There's only one place in the filesystem that actually uses agi_length,
> but let's not leave it vulnerable to the same weird nonsense that
> generates syzbot bugs, eh?
> 
> Signed-off-by: Darrick J. Wong <djwong@kernel.org>
> ---
>  fs/xfs/libxfs/xfs_alloc.c  |   72 ++++++++++++++++++++++++++++----------------
>  fs/xfs/libxfs/xfs_alloc.h  |    3 ++
>  fs/xfs/libxfs/xfs_ialloc.c |   24 +++++++--------
>  3 files changed, 60 insertions(+), 39 deletions(-)

Looks good.

Reviewed-by: Dave Chinner <dchinner@redhat.com>
-- 
Dave Chinner
david@fromorbit.com