Question about inet_rtm_getroute_build_skb()

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 ?

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;
        }

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.

On 8/26/21 9:37 PM, David Ahern wrote:

On 8/26/21 6:16 PM, Eric Dumazet wrote:

quoted

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.

Ah, nice !

Could we add a test for this feature ?
I could not really figure out reading the commit changelog how this stuff was used.

On 8/27/21 8:09 AM, Eric Dumazet wrote:

On 8/26/21 9:37 PM, David Ahern wrote:

quoted

On 8/26/21 6:16 PM, Eric Dumazet wrote:

quoted

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.

Ah, nice !

Could we add a test for this feature ?
I could not really figure out reading the commit changelog how this stuff was used.

tools/testing/selftests/net/fib_rule_tests.sh

I do not see the udp variant, so yes, those should be added.