linux-hardening - Re: [PATCH 02/12] skbuff: Proactively round up to kmalloc bucket size

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Message-ID: <20220922124039.688be0b8@kernel.org>
Date:   Thu, 22 Sep 2022 12:40:39 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Vlastimil Babka <vbabka@...e.cz>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        David Rientjes <rientjes@...gle.com>,
        Pekka Enberg <penberg@...nel.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alex Elder <elder@...nel.org>,
        Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Christian König <christian.koenig@....com>,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Daniel Micay <danielmicay@...il.com>,
        Yonghong Song <yhs@...com>, Marco Elver <elver@...gle.com>,
        Miguel Ojeda <ojeda@...nel.org>,
        Jacob Shin <jacob.shin@....com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-btrfs@...r.kernel.org,
        linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linaro-mm-sig@...ts.linaro.org, linux-fsdevel@...r.kernel.org,
        intel-wired-lan@...ts.osuosl.org, dev@...nvswitch.org,
        x86@...nel.org, linux-wireless@...r.kernel.org,
        llvm@...ts.linux.dev, linux-hardening@...r.kernel.org
Subject: Re: [PATCH 02/12] skbuff: Proactively round up to kmalloc bucket
 size

On Wed, 21 Sep 2022 20:10:03 -0700 Kees Cook wrote:
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 974bbbbe7138..4fe4c7544c1d 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -427,14 +427,15 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask,
>  	 */
>  	size = SKB_DATA_ALIGN(size);
>  	size += SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
> -	data = kmalloc_reserve(size, gfp_mask, node, &pfmemalloc);
> -	if (unlikely(!data))
> -		goto nodata;
> -	/* kmalloc(size) might give us more room than requested.
> +	/* kmalloc(size) might give us more room than requested, so
> +	 * allocate the true bucket size up front.
>  	 * Put skb_shared_info exactly at the end of allocated zone,
>  	 * to allow max possible filling before reallocation.
>  	 */
> -	osize = ksize(data);
> +	osize = kmalloc_size_roundup(size);
> +	data = kmalloc_reserve(osize, gfp_mask, node, &pfmemalloc);
> +	if (unlikely(!data))
> +		goto nodata;
>  	size = SKB_WITH_OVERHEAD(osize);
>  	prefetchw(data + size);

I'd rename osize here to alloc_size for consistency but one could 
argue either way :)

Acked-by: Jakub Kicinski <kuba@...nel.org>