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: 7f639bf869c8 ("bpf: Add socket assign support")
Signed-off-by: Joe Stringer <joe@wand.net.nz>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20200408033540.10339-1-joe@wand.net.nz

diff --git a/net/core/filter.c b/net/core/filter.c
index 7628b947dbc3aabd289fd6f282c82a7faf8e3256..7d6ceaa54d2147584e2033956c4740e4d0ef4af1 100644 (file)
--- 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)))