netdev - [PATCH bpf 4/5] bpf: Set flow flag to allow any source IP in bpf_tunnel

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Date:   Fri, 15 Jul 2022 17:02:31 +0200
From:   Paul Chaignon <paul@...valent.com>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        John Fastabend <john.fastabend@...il.com>,
        Kaixi Fan <fankaixi.li@...edance.com>,
        Nikolay Aleksandrov <razor@...ckwall.org>
Subject: [PATCH bpf 4/5] bpf: Set flow flag to allow any source IP in
 bpf_tunnel_key

Commit 26101f5ab6bd ("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: 26101f5ab6bd ("bpf: Add source ip in "struct bpf_tunnel_key"")
Signed-off-by: Paul Chaignon <paul@...valent.com>
---
 net/core/filter.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/core/filter.c b/net/core/filter.c
index 5d16d66727fc..6d9c800cdab9 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -4641,6 +4641,7 @@ BPF_CALL_4(bpf_skb_set_tunnel_key, struct sk_buff *, skb,
 	info->key.tun_id = cpu_to_be64(from->tunnel_id);
 	info->key.tos = from->tunnel_tos;
 	info->key.ttl = from->tunnel_ttl;
+	info->key.flow_flags = FLOWI_FLAG_ANYSRC;

 	if (flags & BPF_F_TUNINFO_IPV6) {
 		info->mode |= IP_TUNNEL_INFO_IPV6;
-- 
2.25.1