mptcp: change mptcp_established_options() to return opt_size

Instead of passing opt_size address to mptcp_established_options(),
change this function to return it by value.

This removes the need for an expensive stack canary in
tcp_established_options() when CONFIG_STACKPROTECTOR_STRONG=y.

$ scripts/bloat-o-meter -t vmlinux.old vmlinux.new
add/remove: 0/0 grow/shrink: 0/3 up/down: 0/-92 (-92)
Function                                     old     new   delta
tcp_options_write.isra                      1423    1407     -16
mptcp_established_options                   2746    2720     -26
tcp_established_options                      553     503     -50
Total: Before=22110750, After=22110658, chg -0.00%

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20260602125138.2317015-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

3 files changed, 28 insertions, 27 deletions

diff --git a/include/net/mptcp.h b/include/net/mptcp.h
index f7263fe2a2e4..27225c68a388 100644
--- a/include/net/mptcp.h
+++ b/include/net/mptcp.h
@@ -149,9 +149,9 @@ bool mptcp_syn_options(struct sock *sk, const struct sk_buff *skb,
 		       unsigned int *size, struct mptcp_out_options *opts);
 bool mptcp_synack_options(const struct request_sock *req, unsigned int *size,
 			  struct mptcp_out_options *opts);
-bool mptcp_established_options(struct sock *sk, struct sk_buff *skb,
-			       unsigned int *size, unsigned int remaining,
-			       struct mptcp_out_options *opts);
+int mptcp_established_options(struct sock *sk, struct sk_buff *skb,
+			      unsigned int remaining,
+			      struct mptcp_out_options *opts);
 bool mptcp_incoming_options(struct sock *sk, struct sk_buff *skb);
 
 void mptcp_write_options(struct tcphdr *th, __be32 *ptr, struct tcp_sock *tp,
@@ -266,13 +266,12 @@ static inline bool mptcp_synack_options(const struct request_sock *req,
 	return false;
 }
 
-static inline bool mptcp_established_options(struct sock *sk,
-					     struct sk_buff *skb,
-					     unsigned int *size,
-					     unsigned int remaining,
-					     struct mptcp_out_options *opts)
+static inline int mptcp_established_options(struct sock *sk,
+					    struct sk_buff *skb,
+					    unsigned int remaining,
+					    struct mptcp_out_options *opts)
 {
-	return false;
+	return -1;
 }
 
 static inline bool mptcp_incoming_options(struct sock *sk,
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 1b0a066bb6a3..d3b8e61d3c5e 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1183,10 +1183,11 @@ static unsigned int tcp_established_options(struct sock *sk, struct sk_buff *skb
 	 */
 	if (sk_is_mptcp(sk)) {
 		unsigned int remaining = MAX_TCP_OPTION_SPACE - size;
-		unsigned int opt_size = 0;
+		int opt_size;
 
-		if (mptcp_established_options(sk, skb, &opt_size, remaining,
-					      &opts->mptcp)) {
+		opt_size = mptcp_established_options(sk, skb, remaining,
+						     &opts->mptcp);
+		if (opt_size >= 0) {
 			opts->options |= OPTION_MPTCP;
 			size += opt_size;
 		}
diff --git a/net/mptcp/options.c b/net/mptcp/options.c
index 8a1c5698983c..53528301394d 100644
--- a/net/mptcp/options.c
+++ b/net/mptcp/options.c
@@ -836,13 +836,14 @@ static bool mptcp_established_options_mp_fail(struct sock *sk,
 	return true;
 }
 
-bool mptcp_established_options(struct sock *sk, struct sk_buff *skb,
-			       unsigned int *size, unsigned int remaining,
-			       struct mptcp_out_options *opts)
+int mptcp_established_options(struct sock *sk, struct sk_buff *skb,
+			      unsigned int remaining,
+			      struct mptcp_out_options *opts)
 {
 	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
 	struct mptcp_sock *msk = mptcp_sk(subflow->conn);
 	unsigned int opt_size = 0;
+	int total_size = 0;
 	bool snd_data_fin;
 	bool ret = false;
 
@@ -852,20 +853,20 @@ bool mptcp_established_options(struct sock *sk, struct sk_buff *skb,
 	 * option space.
 	 */
 	if (unlikely(__mptcp_check_fallback(msk) && !mptcp_check_infinite_map(skb)))
-		return true;
+		return 0;
 
 	if (unlikely(skb && TCP_SKB_CB(skb)->tcp_flags & TCPHDR_RST)) {
 		if (mptcp_established_options_fastclose(sk, &opt_size, remaining, opts) ||
 		    mptcp_established_options_mp_fail(sk, &opt_size, remaining, opts)) {
-			*size += opt_size;
+			total_size += opt_size;
 			remaining -= opt_size;
 		}
 		/* MP_RST can be used with MP_FASTCLOSE and MP_FAIL if there is room */
 		if (mptcp_established_options_rst(sk, skb, &opt_size, remaining, opts)) {
-			*size += opt_size;
+			total_size += opt_size;
 			remaining -= opt_size;
 		}
-		return true;
+		return total_size;
 	}
 
 	snd_data_fin = mptcp_data_fin_enabled(msk);
@@ -877,9 +878,9 @@ bool mptcp_established_options(struct sock *sk, struct sk_buff *skb,
 		ret = true;
 		if (mptcp_established_options_mp_fail(sk, &mp_fail_size,
 						      remaining - opt_size, opts)) {
-			*size += opt_size + mp_fail_size;
+			total_size += opt_size + mp_fail_size;
 			remaining -= opt_size - mp_fail_size;
-			return true;
+			return total_size;
 		}
 	}
 
@@ -887,27 +888,27 @@ bool mptcp_established_options(struct sock *sk, struct sk_buff *skb,
 	 * TCP option space would be fatal
 	 */
 	if (WARN_ON_ONCE(opt_size > remaining))
-		return false;
+		return -1;
 
-	*size += opt_size;
+	total_size += opt_size;
 	remaining -= opt_size;
 	if (mptcp_established_options_add_addr(sk, skb, &opt_size, remaining, opts)) {
-		*size += opt_size;
+		total_size += opt_size;
 		remaining -= opt_size;
 		ret = true;
 	} else if (mptcp_established_options_rm_addr(sk, &opt_size, remaining, opts)) {
-		*size += opt_size;
+		total_size += opt_size;
 		remaining -= opt_size;
 		ret = true;
 	}
 
 	if (mptcp_established_options_mp_prio(sk, &opt_size, remaining, opts)) {
-		*size += opt_size;
+		total_size += opt_size;
 		remaining -= opt_size;
 		ret = true;
 	}
 
-	return ret;
+	return ret ? total_size : -1;
 }
 
 bool mptcp_synack_options(const struct request_sock *req, unsigned int *size,