FAILED: patch "[PATCH] landlock: Fix TCP Fast Open connection bypass" failed to apply to 7.1-stable tree

The patch below does not apply to the 7.1-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-7.1.y
git checkout FETCH_HEAD
git cherry-pick -x 33cb713db0161b54f04fe830e062c9e102c29a04
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026072133-clapped-variably-21a1@gregkh' --subject-prefix 'PATCH 7.1.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 33cb713db0161b54f04fe830e062c9e102c29a04 Mon Sep 17 00:00:00 2001
From: Matthieu Buffet <[email protected]>
Date: Wed, 1 Jul 2026 23:46:27 +0200
Subject: [PATCH] landlock: Fix TCP Fast Open connection bypass
MIME-Version: 1.0
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Content-Transfer-Encoding: 8bit

The documentation of the socket_connect() LSM hook states that it controls connecting a socket to a remote address. It has not been the case since the addition of TCP Fast Open (RFC 7413) support, which allows opening a TCP connection (thus, setting a socket's destination address) via the MSG_FASTOPEN flag passed to sendto()/sendmsg()/sendmmsg(). The problem then got duplicated into MPTCP.

Landlock did not take it into account when its TCP support was added, leaving a bypass of TCP connect policy.

Ideally a call to the LSM hook would be added in the fastopen code path, in order to fix this generically. But connect() hooks are designed to run with the socket locked, unlike sendmsg() hooks.

index cbff59ec3aba..46c17116fcf4 100644
@@ -351,6 +351,14 @@ static int hook_socket_sendmsg(struct socket *const sock,
 	access_mask_t access_request;
 	int ret = 0;
 
+	if ((msg->msg_flags & MSG_FASTOPEN) && address && sk_is_tcp(sock->sk)) {
+		ret = current_check_access_socket(
+			sock, address, addrlen, LANDLOCK_ACCESS_NET_CONNECT_TCP,
+			true);
+		if (ret != 0)
+			return ret;
+	}
+
 	if (sk_is_udp(sock->sk))
 		access_request = LANDLOCK_ACCESS_NET_CONNECT_SEND_UDP;
 	else