bpf: Set flow flag to allow any source IP in bpf_tunnel_key

Commit 4b4e5af1f714 ("bpf: Add source ip in "struct bpf_tunnel_key"")
added support for getting and setting the outer source IP of encapsulated
packets via the bpf_skb_{get,set}_tunnel_key BPF helper. This change
allows BPF programs to set any IP address as the source, including for
example the IP address of a container running on the same host.

In that last case, however, the encapsulated packets are dropped when
looking up the route because the source IP address isn't assigned to any
interface on the host. To avoid this, we need to set the
FLOWI_FLAG_ANYSRC flag.

Fixes: 4b4e5af1f714 ("bpf: Add source ip in "struct bpf_tunnel_key"")
Signed-off-by: Paul Chaignon <paul@isovalent.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Nikolay Aleksandrov <razor@blackwall.org>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/76873d384e21288abe5767551a0799ac93ec07fb.1658759380.git.paul@isovalent.com

diff --git a/net/core/filter.c b/net/core/filter.c
index 57c5e4c4efd269ad9ab638324e1b8edca754487a..dffc7dcda96acf28aa76a96cce02b95538434baa 100644 (file)
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -4653,6 +4653,7 @@ BPF_CALL_4(bpf_skb_set_tunnel_key, struct sk_buff *, skb,
        } else {
                info->key.u.ipv4.dst = cpu_to_be32(from->remote_ipv4);
                info->key.u.ipv4.src = cpu_to_be32(from->local_ipv4);
+               info->key.flow_flags = FLOWI_FLAG_ANYSRC;
        }
 
        return 0;