netdev - [PATCH bpf] bpf: Fix use of sk->sk_reuseport from sk

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Message-Id: <20200408033540.10339-1-joe@wand.net.nz>
Date:   Tue,  7 Apr 2020 20:35:40 -0700
From:   Joe Stringer <joe@...d.net.nz>
To:     bpf@...r.kernel.org
Cc:     netdev@...r.kernel.org, daniel@...earbox.net, ast@...nel.org
Subject: [PATCH bpf] bpf: Fix use of sk->sk_reuseport from sk_assign

In testing, we found that for request sockets the sk->sk_reuseport field
may yet be uninitialized, which caused bpf_sk_assign() to randomly
succeed or return -ESOCKTNOSUPPORT when handling the forward ACK in a
three-way handshake.

Fix it by only applying the reuseport check for full sockets.

Fixes: cf7fbe660f2d ("bpf: Add socket assign support")
Signed-off-by: Joe Stringer <joe@...d.net.nz>
---
 net/core/filter.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index 7628b947dbc3..7d6ceaa54d21 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -5925,7 +5925,7 @@ BPF_CALL_3(bpf_sk_assign, struct sk_buff *, skb, struct sock *, sk, u64, flags)
 		return -EOPNOTSUPP;
 	if (unlikely(dev_net(skb->dev) != sock_net(sk)))
 		return -ENETUNREACH;
-	if (unlikely(sk->sk_reuseport))
+	if (unlikely(sk_fullsock(sk) && sk->sk_reuseport))
 		return -ESOCKTNOSUPPORT;
 	if (sk_is_refcounted(sk) &&
 	    unlikely(!refcount_inc_not_zero(&sk->sk_refcnt)))
-- 
2.20.1