linux-kernel - [PATCH 5.19 0537/1157] bpf: Set flow flag to allow any source IP in bpf_tunnel

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Date:   Mon, 15 Aug 2022 19:58:13 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Paul Chaignon <paul@...valent.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Nikolay Aleksandrov <razor@...ckwall.org>,
        Martin KaFai Lau <kafai@...com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.19 0537/1157] bpf: Set flow flag to allow any source IP in bpf_tunnel_key

From: Paul Chaignon <paul@...valent.com>

[ Upstream commit b8fff748521c7178b9a7d32b5a34a81cec8396f3 ]

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>
Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
Reviewed-by: Nikolay Aleksandrov <razor@...ckwall.org>
Acked-by: Martin KaFai Lau <kafai@...com>
Link: https://lore.kernel.org/bpf/76873d384e21288abe5767551a0799ac93ec07fb.1658759380.git.paul@isovalent.com
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 net/core/filter.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/core/filter.c b/net/core/filter.c
index 7950f7520765..5978984b752f 100644
--- 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;
-- 
2.35.1