Re: [PATCH 5/6] xfs: fix memcpy fortify errors in EFI log format copying

[Kees Cook <keescook@chromium.org>]

On Mon, Oct 24, 2022 at 02:32:59PM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <djwong@kernel.org>
> 
> Starting in 6.1, CONFIG_FORTIFY_SOURCE checks the length parameter of
> memcpy.  Since we're already fixing problems with BUI item copying, we
> should fix it everything else.
> 
> An extra difficulty here is that the ef[id]_extents arrays are declared
> as single-element arrays.  This is not the convention for flex arrays in
> the modern kernel, and it causes all manner of problems with static
> checking tools, since they often cannot tell the difference between a
> single element array and a flex array.
> 
> So for starters, change those array[1] declarations to array[]
> declarations to signal that they are proper flex arrays and adjust all
> the "size-1" expressions to fit the new declaration style.

This looks very familiar! :)

https://lore.kernel.org/linux-xfs/20210419082804.2076124-1-hch@lst.de/

It seems like it might make more sense to start with hch's series, and
see what's missing?

> 
> Next, refactor the xfs_efi_copy_format function to handle the copying of
> the head and the flex array members separately.  While we're at it, fix
> a minor validation deficiency in the recovery function.

This feels like 3 separate logical changes in a single patch, but,
regardless:

Reviewed-by: Kees Cook <keescook@chromium.org>

This will proactively fix XFS under CONFIG_UBSAN_BOUNDS once
-fstrict-flex-arrays is added. Thank you!

-- 
Kees Cook