netdev - Re: Question about inet_rtm_getroute_build

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Date:   Thu, 26 Aug 2021 21:37:13 -0700
From:   David Ahern <dsahern@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>,
        Networking <netdev@...r.kernel.org>,
        Roopa Prabhu <roopa@...dia.com>
Subject: Re: Question about inet_rtm_getroute_build_skb()

On 8/26/21 6:16 PM, Eric Dumazet wrote:
> Hi Roopa
> 
> I noticed inet_rtm_getroute_build_skb() has this endian issue 
> when building an UDP header.
> 
> Would the following fix break user space ?

I do not see how. As I recall this is only for going through
ip_route_input_rcu and ip_route_output_key_hash_rcu and a call to
fib4_rules_early_flow_dissect.

> 
> Thanks.
> 
> diff --git a/net/ipv4/route.c b/net/ipv4/route.c
> index a6f20ee3533554b210d27c4ab6637ca7a05b148b..50133b935f868c2ae9474eea027a0ad864a43936 100644
> --- a/net/ipv4/route.c
> +++ b/net/ipv4/route.c
> @@ -3170,7 +3170,7 @@ static struct sk_buff *inet_rtm_getroute_build_skb(__be32 src, __be32 dst,
>                 udph = skb_put_zero(skb, sizeof(struct udphdr));
>                 udph->source = sport;
>                 udph->dest = dport;
> -               udph->len = sizeof(struct udphdr);
> +               udph->len = htons(sizeof(struct udphdr));
>                 udph->check = 0;
>                 break;
>         }
>