linux-kernel - Re: [PATCH -next] mux: convert mux

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Date: Fri, 23 Feb 2024 15:52:56 -0800
From: Kees Cook <keescook@...omium.org>
To: Jacob Keller <jacob.e.keller@...el.com>
Cc: Jesse Brandeburg <jesse.brandeburg@...el.com>,
	Peter Rosin <peda@...ntia.se>, gustavoars@...nel.org,
	linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org
Subject: Re: [PATCH -next] mux: convert mux_chip->mux to flexible array

On Tue, Feb 20, 2024 at 01:27:45PM -0800, Jacob Keller wrote:
> 
> 
> On 2/18/2024 9:04 PM, Kees Cook wrote:
> > On Mon, Feb 27, 2023 at 12:28:43PM -0800, Jesse Brandeburg wrote:
> >> On 2/22/2023 5:42 PM, Jacob Keller wrote:
> >>> The mux_chip structure size is over allocated to additionally include both
> >>> the array of mux controllers as well as a device specific private area.
> >>> The controllers array is then pointed to by assigning mux_chip->mux to the
> >>> first block of extra memory, while the private area is extracted via
> >>> mux_chip_priv() and points to the area just after the controllers.
> >>>
> >>> The size of the mux_chip allocation uses direct multiplication and addition
> >>> rather than the <linux/overflow.h> helpers. In addition, the mux_chip->mux
> >>> struct member wastes space by having to store the pointer as part of the
> >>> structures.
> >>>
> >>> Convert struct mux_chip to use a flexible array member for the mux
> >>> controller array. Use struct_size() and size_add() to compute the size of
> >>> the structure while protecting against overflow.
> >>>
> >>> After converting the mux pointer, notice that two 4-byte holes remain in
> >>> the structure layout due to the alignment requirements for the dev
> >>> sub-structure and the ops pointer.
> >>>
> >>> These can be easily fixed through re-ordering the id field to the 4-byte
> >>> hole just after the controllers member.
> >>
> >> Looks good to me (just a driver dev, not a mux dev!). Also added
> >> linux-i2c mailing list and a couple others for more review.
> >>
> >> Reviewed-by: Jesse Brandeburg <jesse.brandeburg@...el.com>
> >>
> >> related thread (cocci script) at [1]
> >>
> >> [1]
> >> https://lore.kernel.org/all/20230227202428.3657443-1-jacob.e.keller@intel.com/
> > 
> > *thread necromancy*
> > 
> > Can we land this? It's the last struct_size() instance that the above
> > Coccinelle script flags.
> > 
> > Reviewed-by: Kees Cook <keescook@...omium.org>
> > 
> 
> I'm happy to send a v2 if we need.

Since it's been a while, yeah, can you send a v2?

Thanks!

-Kees

-- 
Kees Cook