bpf, sockmap: Fix data loss caused by using apply_bytes on ingress redirect

Use apply_bytes on ingress redirect, when apply_bytes is less than
the length of msg data, some data may be skipped and lost in
bpf_tcp_ingress().

If there is still data in the scatterlist that has not been consumed,
we cannot move the msg iter.

Fixes: 604326b4 ("bpf, sockmap: convert to generic sk_msg interface")
Signed-off-by: Pengcheng Yang <yangpc@wangsu.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Jakub Sitnicki <jakub@cloudflare.com>
Link: https://lore.kernel.org/bpf/1669718441-2654-4-git-send-email-yangpc@wangsu.com

net/ipv4/tcp_bpf.c

@@ -45,8 +45,11 @@ static int bpf_tcp_ingress(struct sock *sk, struct sk_psock *psock,
 		tmp->sg.end = i;
 		if (apply) {
 			apply_bytes -= size;
-			if (!apply_bytes)
+			if (!apply_bytes) {
+				if (sge->length)
+					sk_msg_iter_var_prev(i);
 				break;
+			}
 		}
 	} while (i != msg->sg.end);