sock: Introduce sk_set_prio_allowed helper function

Simplify priority setting permissions with the 'sk_set_prio_allowed'
function, centralizing the validation logic. This change is made in
anticipation of a second caller in a following patch.
No functional changes.

Reviewed-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Suggested-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Anna Emese Nyiri <annaemesenyiri@gmail.com>
Link: https://patch.msgid.link/20241213084457.45120-2-annaemesenyiri@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/core/sock.c

@@ -454,6 +454,13 @@ static int sock_set_timeout(long *timeo_p, sockptr_t optval, int optlen,
 	return 0;
 }
 
+static bool sk_set_prio_allowed(const struct sock *sk, int val)
+{
+	return ((val >= TC_PRIO_BESTEFFORT && val <= TC_PRIO_INTERACTIVE) ||
+		sockopt_ns_capable(sock_net(sk)->user_ns, CAP_NET_RAW) ||
+		sockopt_ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN));
+}
+
 static bool sock_needs_netstamp(const struct sock *sk)
 {
 	switch (sk->sk_family) {
@@ -1193,9 +1200,7 @@ int sk_setsockopt(struct sock *sk, int level, int optname,
 	/* handle options which do not require locking the socket. */
 	switch (optname) {
 	case SO_PRIORITY:
-		if ((val >= 0 && val <= 6) ||
-		    sockopt_ns_capable(sock_net(sk)->user_ns, CAP_NET_RAW) ||
-		    sockopt_ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN)) {
+		if (sk_set_prio_allowed(sk, val)) {
 			sock_set_priority(sk, val);
 			return 0;
 		}