[PATCH net] tcp: check space before adding MPTCP SYN options

[PATCH net] tcp: check space before adding MPTCP SYN options

[Matthieu Baerts (NGI0)]

From: MoYuanhao <moyuanhao3676@163.com>

Ensure there is enough space before adding MPTCP options in
tcp_syn_options().

Without this check, 'remaining' could underflow, and causes issues. If
there is not enough space, MPTCP should not be used.

Signed-off-by: MoYuanhao <moyuanhao3676@163.com>
Fixes: cec37a6e41aa ("mptcp: Handle MP_CAPABLE options for outgoing connections")
Cc: stable@vger.kernel.org
Acked-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
[ Matt: Add Fixes, cc Stable, update Description ]
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 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 5485a70b5fe5a6039d19f4321c3c2ec8ecc6ffea..0e5b9a654254b32907ee9739f3443791104bd611 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;
+			}
 		}
 	}
 

---
base-commit: 09310cfd4ea5c3ab2c7a610420205e0a1660bf7e
change-id: 20241209-net-mptcp-check-space-syn-5694196ffb5f

Best regards,
-- 
Matthieu Baerts (NGI0) <matttbe@kernel.org>

Re: [PATCH net] tcp: check space before adding MPTCP SYN options

[Eric Dumazet]

On Mon, Dec 9, 2024 at 1:28 PM Matthieu Baerts (NGI0)
<matttbe@kernel.org> wrote:
>
> From: MoYuanhao <moyuanhao3676@163.com>
>
> Ensure there is enough space before adding MPTCP options in
> tcp_syn_options().
>
> Without this check, 'remaining' could underflow, and causes issues. If
> there is not enough space, MPTCP should not be used.
>
> Signed-off-by: MoYuanhao <moyuanhao3676@163.com>
> Fixes: cec37a6e41aa ("mptcp: Handle MP_CAPABLE options for outgoing connections")
> Cc: stable@vger.kernel.org
> Acked-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
> [ Matt: Add Fixes, cc Stable, update Description ]
> Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>

Reviewed-by: Eric Dumazet <edumazet@google.com>

Re: [PATCH net] tcp: check space before adding MPTCP SYN options

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Mon, 09 Dec 2024 13:28:14 +0100 you wrote:
> From: MoYuanhao <moyuanhao3676@163.com>
> 
> Ensure there is enough space before adding MPTCP options in
> tcp_syn_options().
> 
> Without this check, 'remaining' could underflow, and causes issues. If
> there is not enough space, MPTCP should not be used.
> 
> [...]

Here is the summary with links:
  - [net] tcp: check space before adding MPTCP SYN options
    https://git.kernel.org/netdev/net/c/06d64ab46f19

You are awesome, thank you!
-- 
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