netdev - Re: [PATCH v2 1/1] net: ipv4: fix return value check in esp_remove

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Date: Tue, 25 Jul 2023 10:44:50 -0700
From: Alexander H Duyck <alexander.duyck@...il.com>
To: Yuanjun Gong <ruc_gongyuanjun@....com>, dsahern@...nel.org
Cc: herbert@...dor.apana.org.au, netdev@...r.kernel.org, 
	steffen.klassert@...unet.com
Subject: Re: [PATCH v2 1/1] net: ipv4: fix return value check in
 esp_remove_trailer()

On Tue, 2023-07-25 at 14:40 +0800, Yuanjun Gong wrote:
> return an error number if an unexpected result is returned by
> pskb_tirm() in esp_remove_trailer().
> 
> Signed-off-by: Yuanjun Gong <ruc_gongyuanjun@....com>
> ---
>  net/ipv4/esp4.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/net/ipv4/esp4.c b/net/ipv4/esp4.c
> index ba06ed42e428..b435e3fe4dc6 100644
> --- a/net/ipv4/esp4.c
> +++ b/net/ipv4/esp4.c
> @@ -732,7 +732,9 @@ static inline int esp_remove_trailer(struct sk_buff *skb)
>  		skb->csum = csum_block_sub(skb->csum, csumdiff,
>  					   skb->len - trimlen);
>  	}
> -	pskb_trim(skb, skb->len - trimlen);
> +	ret = pskb_trim(skb, skb->len - trimlen);
> +	if (ret)
> +		goto out;
>  
>  	ret = nexthdr[1];
>  

In what case would you encounter this error? From what I can tell it
looks like there are checks in the callers, specifically the call to
pskb_may_pull() at the start of esp_input() that will go through and
automatically eliminate all the potential reasons for this to fail. So
I am not sure what the point is in adding exception handling for an
exception that is already handled.