From ce5f6f71b029f6a96267a7d876da4a055d7d1611 Mon Sep 17 00:00:00 2001 From: "Matthieu Baerts (NGI0)" Date: Mon, 13 May 2024 18:13:27 -0700 Subject: [PATCH] mptcp: sockopt: info: stop early if no buffer Up to recently, it has been recommended to use getsockopt(MPTCP_INFO) to check if a fallback to TCP happened, or if the client requested to use MPTCP. In this case, the userspace app is only interested by the returned value of the getsocktop() call, and can then give 0 for the option length, and NULL for the buffer address. An easy optimisation is then to stop early, and avoid filling a local buffer -- which now requires two different locks -- if it is not needed. Reviewed-by: Mat Martineau Signed-off-by: Matthieu Baerts (NGI0) Signed-off-by: Mat Martineau Link: https://lore.kernel.org/r/20240514011335.176158-4-martineau@kernel.org Signed-off-by: Jakub Kicinski --- net/mptcp/sockopt.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/net/mptcp/sockopt.c b/net/mptcp/sockopt.c index fcca9433c858..a77b33488176 100644 --- a/net/mptcp/sockopt.c +++ b/net/mptcp/sockopt.c @@ -999,6 +999,10 @@ static int mptcp_getsockopt_info(struct mptcp_sock *msk, char __user *optval, in if (get_user(len, optlen)) return -EFAULT; + /* When used only to check if a fallback to TCP happened. */ + if (len == 0) + return 0; + len = min_t(unsigned int, len, sizeof(struct mptcp_info)); mptcp_diag_fill_info(msk, &m_info); -- 2.39.5