From e681c5a824a98abfcb97f9bad88a5a75cca0cffe Mon Sep 17 00:00:00 2001 From: MoYuanhao Date: Mon, 9 Dec 2024 13:28:14 +0100 Subject: [PATCH] tcp: check space before adding MPTCP SYN options commit 06d64ab46f19ac12f59a1d2aa8cd196b2e4edb5b upstream. 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 Fixes: cec37a6e41aa ("mptcp: Handle MP_CAPABLE options for outgoing connections") Cc: stable@vger.kernel.org Acked-by: Matthieu Baerts (NGI0) [ Matt: Add Fixes, cc Stable, update Description ] Signed-off-by: Matthieu Baerts (NGI0) Reviewed-by: Eric Dumazet Link: https://patch.msgid.link/20241209-net-mptcp-check-space-syn-v1-1-2da992bb6f74@kernel.org Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman --- 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 3f54b76bc281..40568365cdb3 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -827,8 +827,10 @@ 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; + } } }