net: tls: fix marking packets as decrypted

For TLS offload we mark packets with skb->decrypted to make sure
they don't escape the host without getting encrypted first.
The crypto state lives in the socket, so it may get detached
by a call to skb_orphan(). As a safety check - the egress path
drops all packets with skb->decrypted and no "crypto-safe" socket.

The skb marking was added to sendpage only (and not sendmsg),
because tls_device injected data into the TCP stack using sendpage.
This special case was missed when sendpage got folded into sendmsg.

Fixes: c5c37af ("tcp: Convert do_tcp_sendpages() to use MSG_SPLICE_PAGES")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20240530232607.82686-1-kuba@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

net/ipv4/tcp.c

@@ -1165,6 +1165,9 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
 
 			process_backlog++;
 
+#ifdef CONFIG_SKB_DECRYPTED
+			skb->decrypted = !!(flags & MSG_SENDPAGE_DECRYPTED);
+#endif
 			tcp_skb_entail(sk, skb);
 			copy = size_goal;