bpf, sockmap: Do not ignore orig_len parameter

Currently, sk_psock_verdict_recv() returns skb->len

This is problematic because tcp_read_sock() might have
passed orig_len < skb->len, due to the presence of TCP urgent data.

This causes an infinite loop from tcp_read_sock()

Followup patch will make tcp_read_sock() more robust vs bad actors.

Fixes: ef565928 ("bpf, sockmap: Allow skipping sk_skb parser program")
Reported-by: Nsyzbot <syzkaller@googlegroups.com>
Signed-off-by: NEric Dumazet <edumazet@google.com>
Acked-by: NJohn Fastabend <john.fastabend@gmail.com>
Acked-by: NJakub Sitnicki <jakub@cloudflare.com>
Tested-by: NJakub Sitnicki <jakub@cloudflare.com>
Acked-by: NDaniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/r/20220302161723.3910001-1-eric.dumazet@gmail.comSigned-off-by: NJakub Kicinski <kuba@kernel.org>

net/core/skmsg.c

@@ -1153,7 +1153,7 @@ static int sk_psock_verdict_recv(read_descriptor_t *desc, struct sk_buff *skb,
 	struct sk_psock *psock;
 	struct bpf_prog *prog;
 	int ret = __SK_DROP;
-	int len = skb->len;
+	int len = orig_len;
 
 	/* clone here so sk_eat_skb() in tcp_read_sock does not drop our data */
 	skb = skb_clone(skb, GFP_ATOMIC);