linux-kernel - Re: [PATCH v4 7/8] net-device: Use new helpers from overflow.h in netdevice APIs

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Date: Thu, 29 Feb 2024 11:08:58 -0800
From: Kees Cook <keescook@...omium.org>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Vinod Koul <vkoul@...nel.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Jonathan Cameron <Jonathan.Cameron@...wei.com>,
	Mark Brown <broonie@...nel.org>,
	linux-arm-kernel@...ts.infradead.org, dmaengine@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org,
	linux-spi@...r.kernel.org, netdev@...r.kernel.org,
	linux-hardening@...r.kernel.org,
	Jonathan Cameron <jic23@...nel.org>,
	Lars-Peter Clausen <lars@...afoo.de>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>
Subject: Re: [PATCH v4 7/8] net-device: Use new helpers from overflow.h in
 netdevice APIs

On Wed, Feb 28, 2024 at 04:56:09PM -0800, Jakub Kicinski wrote:
> On Wed, 28 Feb 2024 16:01:49 -0800 Kees Cook wrote:
> > So, I found several cases where struct net_device is included in the
> > middle of another structure, which makes my proposal more awkward. But I
> > also don't understand why it's in the _middle_. Shouldn't it always be
> > at the beginning (with priv stuff following it?)
> > Quick search and examined manually: git grep 'struct net_device [a-z0-9_]*;'
> > 
> > struct rtw89_dev
> > struct ath10k
> > etc.
> 
> Ugh, yes, the (ab)use of NAPI.
> 
> > Some even have two included (?)
> 
> And some seem to be cargo-culted from out-of-tree code and are unused :S

Ah, which can I remove?

> That's... less pretty. I'd rather push the ugly into the questionable
> users. Make them either allocate the netdev dynamically and store 
> a pointer, or move the netdev to the end of the struct.
> 
> But yeah, that's a bit of a cleanup :(

So far, it's not too bad. I'm doing some test builds now.


As a further aside, this code:

        struct net_device *dev;
	...
        struct net_device *p;
	...
        /* ensure 32-byte alignment of whole construct */
        alloc_size += NETDEV_ALIGN - 1;
        p = kvzalloc(alloc_size, GFP_KERNEL_ACCOUNT | __GFP_RETRY_MAYFAIL);
	...
        dev = PTR_ALIGN(p, NETDEV_ALIGN);

Really screams for a dynamic-sized (bucketed) kmem_cache_alloc
API. Alignment constraints can be described in a regular kmem_cache
allocator (rather than this open-coded version). I've been intending to
build that for struct msg_msg for a while now, and here's another user. :)

-Kees

-- 
Kees Cook