[PATCH 13/13] bpf: Fix use of sk->sk_reuseport from sk_assign

[Kleber Souza]

On 31.08.20 06:03, Khalid Elmously wrote:
> From: Joe Stringer <joe at wand.net.nz>

This patch is missing:

BugLink: https://bugs.launchpad.net/bugs/1887740

> 
> [ upstream commit 8e368dc72e86ad1e1a612416f32d5ad22dca88bc ]
> 
> 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 at wand.net.nz>
> Signed-off-by: Daniel Borkmann <daniel at iogearbox.net>
> Acked-by: Martin KaFai Lau <kafai at fb.com>
> Link: https://lore.kernel.org/bpf/20200408033540.10339-1-joe@wand.net.nz
> Signed-off-by: Daniel Borkmann <daniel at iogearbox.net>
> Signed-off-by: Khalid Elmously <khalid.elmously at canonical.com>
> ---
>  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 baaeab75327c..a895e272d75e 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -5992,7 +5992,7 @@ 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)))
>