On Sun, Aug 3, 2025 at 10:54 AM Jason Xing kerneljasonxing@gmail.com wrote:
On Sun, Aug 3, 2025 at 9:59 AM Menglong Dong menglong8.dong@gmail.com wrote:
On Sat, Aug 2, 2025 at 9:06 PM Jason Xing kerneljasonxing@gmail.com wrote:
Hi Menglong,
On Sat, Aug 2, 2025 at 5:28 PM Menglong Dong menglong8.dong@gmail.com wrote:
For now, the tcp socket lookup will terminate if the socket is reuse port in inet_lhash2_lookup(), which makes the socket is not the best match.
For example, we have socket1 and socket2 both listen on "0.0.0.0:1234", but socket1 bind on "eth0". We create socket1 first, and then socket2. Then, all connections will goto socket2, which is not expected, as socket1 has higher priority.
This can cause unexpected behavior if TCP MD5 keys is used, as described in Documentation/networking/vrf.rst -> Applications.
Therefor, we lookup the best matched socket first, and then do the reuse
s/Therefor/Therefore
port logic. This can increase some overhead if there are many reuse port socket :/
Fixes: c125e80b8868 ("soreuseport: fast reuseport TCP socket selection") Signed-off-by: Menglong Dong dongml2@chinatelecom.cn
v3:
- use the approach in V1
- add the Fixes tag
net/ipv4/inet_hashtables.c | 13 +++++++------ net/ipv6/inet6_hashtables.c | 13 +++++++------ 2 files changed, 14 insertions(+), 12 deletions(-)
diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c index ceeeec9b7290..51751337f394 100644 --- a/net/ipv4/inet_hashtables.c +++ b/net/ipv4/inet_hashtables.c @@ -389,17 +389,18 @@ static struct sock *inet_lhash2_lookup(const struct net *net, sk_nulls_for_each_rcu(sk, node, &ilb2->nulls_head) { score = compute_score(sk, net, hnum, daddr, dif, sdif); if (score > hiscore) {
result = inet_lookup_reuseport(net, sk, skb, doff,saddr, sport, daddr, hnum, inet_ehashfn);if (result)return result;result = sk; hiscore = score; } }return result;
if (!result)return NULL;sk = inet_lookup_reuseport(net, result, skb, doff,saddr, sport, daddr, hnum, inet_ehashfn);return sk ? sk : result;}
IMHO, I don't see it as a bugfix. So can you elaborate on what the exact side effect you're faced with is when the algorithm finally prefers socket2 (without this patch)?
Hi, Jason. The case is that the user has several NIC, and there are some sockets that are binded to them, who listen on TCP port 6666. And a global socket doesn't bind any NIC and listens on TCP port 6666.
In theory, the connection request from the NIC will goto the listen socket that is binded on it. When on socket is binded on the NIC, it goto the global socket. However, the connection request always goto the global socket, which is not expected.
What's worse is that when TCP MD5 is used on the socket, the connection will fail :/
I'm trying to picture what the usage can be in the userland as you pointed out in the MD5 case. As to the client side, it seems weird since it cannot detect and know the priority of the other side where a few sockets listen on the same address and port.
For the server side, it needs to add all the clients information with the TCP_MD5SIG option. For socket1 that binded on the eth0, it will add all the client addresses that come from eth0 to the socket1 with TCP_MD5SIG. So the server knows the clients.
And in my use case, the TCP MD5 + VRF is used. The details are a little fuzzy for me, which I need to do some recalling :/
I'm not saying the priority problem doesn't exist, just not knowing how severe the case could be. It doesn't look that bad at least until now. Only the selection policy itself matters more to the server side than to the client side.
Thanks, Jason