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@163.com>
---
 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

On Wed, Dec 4, 2024 at 5:07 AM MoYuanhao <moyuanhao3676@163.com> wrote:
>
> 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@163.com>
> ---

If this is happening, then this would be a bug, and a Fixes: tag would
be needed.

If this is not yet happening, but would happen in the future, this
patch would hide a bug.

You forgot to CC MPTCP maintainers and reviewers ?

Matthieu Baerts <matttbe@kernel.org> (maintainer:NETWORKING [MPTCP])
Mat Martineau <martineau@kernel.org> (maintainer:NETWORKING [MPTCP])
Geliang Tang <geliang@kernel.org> (reviewer:NETWORKING [MPTCP])

In my  opinion, we should pass @remaining to mptcp_syn_options()
arguments to avoid side effects.