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

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Message-ID: <202402182100.1D5BBE45@keescook>
Date: Sun, 18 Feb 2024 21:04:03 -0800
From: Kees Cook <keescook@...omium.org>
To: Jesse Brandeburg <jesse.brandeburg@...el.com>
Cc: Jacob Keller <jacob.e.keller@...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 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>

-- 
Kees Cook