From: Matthieu Buffet Date: Wed, 1 Jul 2026 21:46:27 +0000 (+0200) Subject: landlock: Fix TCP Fast Open connection bypass X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=33cb713db0161b54f04fe830e062c9e102c29a04;p=thirdparty%2Fkernel%2Flinux.git landlock: Fix TCP Fast Open connection bypass 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. Closes: https://github.com/landlock-lsm/linux/issues/41 Fixes: fff69fb03dde ("landlock: Support network rules with TCP bind and connect") Signed-off-by: Matthieu Buffet Link: https://patch.msgid.link/20260701214628.33319-1-matthieu@buffet.re Cc: stable@vger.kernel.org [mic: Wrap commit message] Signed-off-by: Mickaël Salaün --- diff --git a/security/landlock/net.c b/security/landlock/net.c index cbff59ec3abaa..46c17116fcf42 100644 --- a/security/landlock/net.c +++ b/security/landlock/net.c @@ -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