[PATCH net-next] tcp: Check space before adding MPTCP options

[MoYuanhao]

Ensure enough space before adding MPTCP options in tcp_syn_options()
Added a check to verify sufficient remaining space
before inserting MPTCP options in SYN packets.
This prevents issues when space is insufficient.

Signed-off-by: MoYuanhao <moyuanhao3676@xxxxxxx>
---
 net/ipv4/tcp_output.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 5485a70b5fe5..0e5b9a654254 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -883,8 +883,10 @@ static unsigned int tcp_syn_options(struct sock *sk, struct sk_buff *skb,
 		unsigned int size;
 
 		if (mptcp_syn_options(sk, skb, &size, &opts->mptcp)) {
-			opts->options |= OPTION_MPTCP;
-			remaining -= size;
+			if (remaining >= size) {
+				opts->options |= OPTION_MPTCP;
+				remaining -= size;
+			}
 		}
 	}
 
-- 
2.25.1