diff mbox series

[net-next,v2,3/8] mptcp: sockopt: info: stop early if no buffer

Message ID 20240514011335.176158-4-martineau@kernel.org (mailing list archive)
State Mainlined, archived
Delegated to: Mat Martineau
Headers show
Series mptcp: small improvements, fix and clean-ups | expand

Commit Message

Mat Martineau May 14, 2024, 1:13 a.m. UTC 
From: "Matthieu Baerts (NGI0)" <matttbe@kernel.org>

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 <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Mat Martineau <martineau@kernel.org>
---
 net/mptcp/sockopt.c | 4 ++++
 1 file changed, 4 insertions(+)
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Patch

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);