On Sun, Jul 26, 2020 at 02:02:28PM +0200, Jakub Sitnicki wrote:
> When BPF sk lookup invokes reuseport handling for the selected socket, it
> should ignore the fact that reuseport group can contain connected UDP
> sockets. With BPF sk lookup this is not relevant as we are not scoring
> sockets to find the best match, which might be a connected UDP socket.
>
> Fix it by unconditionally accepting the socket selected by reuseport.
>
> This fixes the following two failures reported by test_progs.
>
> # ./test_progs -t sk_lookup
> ...
> #73/14 UDP IPv4 redir and reuseport with conns:FAIL
> ...
> #73/20 UDP IPv6 redir and reuseport with conns:FAIL
> ...
>
> Fixes: a57066b1a019 ("Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net")
> Cc: David S. Miller <davem@xxxxxxxxxxxxx>
> Reported-by: Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx>
> Signed-off-by: Jakub Sitnicki <jakub@xxxxxxxxxxxxxx>
> ---
> net/ipv4/udp.c | 2 +-
> net/ipv6/udp.c | 2 +-
> 2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> index 7ce31beccfc2..e88efba07551 100644
> --- a/net/ipv4/udp.c
> +++ b/net/ipv4/udp.c
> @@ -473,7 +473,7 @@ static struct sock *udp4_lookup_run_bpf(struct net *net,
> return sk;
>
> reuse_sk = lookup_reuseport(net, sk, skb, saddr, sport, daddr, hnum);
> - if (reuse_sk && !reuseport_has_conns(sk, false))
> + if (reuse_sk)
> sk = reuse_sk;
> return sk;
> }
> diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
> index c394e674f486..29d9691359b9 100644
> --- a/net/ipv6/udp.c
> +++ b/net/ipv6/udp.c
> @@ -208,7 +208,7 @@ static inline struct sock *udp6_lookup_run_bpf(struct net *net,
> return sk;
>
> reuse_sk = lookup_reuseport(net, sk, skb, saddr, sport, daddr, hnum);
> - if (reuse_sk && !reuseport_has_conns(sk, false))
> + if (reuse_sk)
>From __udp[46]_lib_lookup,
1. The connected udp is picked by the kernel first.
If a 4-tuple-matched connected udp is found. It should have already
been returned there.
2. If kernel cannot find a connected udp, the sk-lookup bpf prog can
get a chance to pick another socket (likely bound to a different
IP/PORT that the packet is destinated to) by bpf_sk_lookup_assign().
However, bpf_sk_lookup_assign() does not allow TCP_ESTABLISHED.
With the change in this patch, it then allows the reuseport-bpf-prog
to pick a connected udp which cannot be found in step (1). Can you
explain a use case for this?
