linux-kernel - Re: [PATCH net-next v10 10/14] net: add support for skbs with unreadable frags

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Date: Tue, 04 Jun 2024 12:46:01 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Mina Almasry <almasrymina@...gle.com>, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org, 
	linux-alpha@...r.kernel.org, linux-mips@...r.kernel.org, 
	linux-parisc@...r.kernel.org, sparclinux@...r.kernel.org, 
	linux-trace-kernel@...r.kernel.org, linux-arch@...r.kernel.org, 
	bpf@...r.kernel.org, linux-kselftest@...r.kernel.org, 
	linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org
Cc: "David S. Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>,  Jakub Kicinski <kuba@...nel.org>, Donald Hunter
 <donald.hunter@...il.com>, Jonathan Corbet <corbet@....net>, Richard
 Henderson <richard.henderson@...aro.org>, Ivan Kokshaysky
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Subject: Re: [PATCH net-next v10 10/14] net: add support for skbs with
 unreadable frags

On Thu, 2024-05-30 at 20:16 +0000, Mina Almasry wrote:
> diff --git a/net/core/gro.c b/net/core/gro.c
> index 26f09c3e830b7..7b9d018f552bd 100644
> --- a/net/core/gro.c
> +++ b/net/core/gro.c
> @@ -422,6 +422,9 @@ static void gro_pull_from_frag0(struct sk_buff *skb, int grow)
>  {
>  	struct skb_shared_info *pinfo = skb_shinfo(skb);
>  
> +	if (WARN_ON_ONCE(!skb_frags_readable(skb)))
> +		return;
> +
>  	BUG_ON(skb->end - skb->tail < grow);
>  
>  	memcpy(skb_tail_pointer(skb), NAPI_GRO_CB(skb)->frag0, grow);
> @@ -443,7 +446,7 @@ static void gro_try_pull_from_frag0(struct sk_buff *skb)
>  {
>  	int grow = skb_gro_offset(skb) - skb_headlen(skb);
>  
> -	if (grow > 0)
> +	if (grow > 0 && skb_frags_readable(skb))
>  		gro_pull_from_frag0(skb, grow);
>  }

I'm unsure if this was already mentioned, so please pardon the eventual
duplicate...

The above code is quite critical performance wise, and the previous
patch already prevent frag0 from being set to a non paged frag, so what
about dropping the above additional checks?

thanks!

Paolo