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

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Date: Tue, 20 Feb 2024 13:27:45 -0800
From: Jacob Keller <jacob.e.keller@...el.com>
To: Kees Cook <keescook@...omium.org>, Jesse Brandeburg
	<jesse.brandeburg@...el.com>
CC: 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 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.

Thanks,
Jake