netdev - Re: [PATCH 5.15.y 1/2] net: add pskb_may_pull

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Message-ID: <2024100856-skittle-hazy-9569@gregkh>
Date: Tue, 8 Oct 2024 12:36:28 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: Sherry Yang <sherry.yang@...cle.com>
Cc: stable@...r.kernel.org, sashal@...nel.org, kuba@...nel.org,
	roopa@...dia.com, nikolay@...dia.com, davem@...emloft.net,
	bridge@...ts.linux-foundation.org, netdev@...r.kernel.org
Subject: Re: [PATCH 5.15.y 1/2] net: add pskb_may_pull_reason() helper

On Fri, Oct 04, 2024 at 10:03:27AM -0700, Sherry Yang wrote:
> From: Eric Dumazet <edumazet@...gle.com>
> 
> [ Upstream commit 1fb2d41501f38192d8a19da585cd441cf8845697 ]
> 
> pskb_may_pull() can fail for two different reasons.
> 
> Provide pskb_may_pull_reason() helper to distinguish
> between these reasons.
> 
> It returns:
> 
> SKB_NOT_DROPPED_YET           : Success
> SKB_DROP_REASON_PKT_TOO_SMALL : packet too small
> SKB_DROP_REASON_NOMEM         : skb->head could not be resized
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reviewed-by: David Ahern <dsahern@...nel.org>
> Signed-off-by: Jakub Kicinski <kuba@...nel.org>
> Stable-dep-of: 8bd67ebb50c0 ("net: bridge: xmit: make sure we have at least eth header len bytes")
> Signed-off-by: Sasha Levin <sashal@...nel.org>
> [Sherry: bp to 5.15.y. Minor conflicts due to missing commit
> d427c8999b07 ("net-next: skbuff: refactor pskb_pull") which is not
> necessary in 5.15.y. Ignore context change.
> Signed-off-by: Sherry Yang <sherry.yang@...cle.com>
> ---
>  include/linux/skbuff.h | 19 +++++++++++++++----
>  1 file changed, 15 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index b230c422dc3b..f92e8fe4f5eb 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -2465,13 +2465,24 @@ static inline void *pskb_pull(struct sk_buff *skb, unsigned int len)
>  	return unlikely(len > skb->len) ? NULL : __pskb_pull(skb, len);
>  }
>  
> -static inline bool pskb_may_pull(struct sk_buff *skb, unsigned int len)
> +static inline enum skb_drop_reason
> +pskb_may_pull_reason(struct sk_buff *skb, unsigned int len)
>  {
>  	if (likely(len <= skb_headlen(skb)))
> -		return true;
> +		return SKB_NOT_DROPPED_YET;
> +
>  	if (unlikely(len > skb->len))
> -		return false;
> -	return __pskb_pull_tail(skb, len - skb_headlen(skb)) != NULL;
> +		return SKB_DROP_REASON_PKT_TOO_SMALL;
> +
> +	if (unlikely(!__pskb_pull_tail(skb, len - skb_headlen(skb))))
> +		return SKB_DROP_REASON_NOMEM;
> +
> +	return SKB_NOT_DROPPED_YET;
> +}
> +
> +static inline bool pskb_may_pull(struct sk_buff *skb, unsigned int len)
> +{
> +	return pskb_may_pull_reason(skb, len) == SKB_NOT_DROPPED_YET;
>  }
>  
>  void skb_condense(struct sk_buff *skb);
> -- 
> 2.46.0
> 
> 

Any specific reason why you didn't test build this patch?

It breaks the build into thousands of tiny pieces.

greg k-h