From eb8ea9a7c5b3d0c3576bf2553be208b8ebf027b4 Mon Sep 17 00:00:00 2001
From: Florian Eckert <fe@dev.tdt.de>
Date: Tue, 29 Sep 2026 15:48:21 +0200
Subject: [PATCH] strongswan: support additional key exchange methods

With peers that support multiple IKEv2 key exchanges (RFC 9370), up
to seven additional key exchanges may be negotiated. strongSwan
configures them by prefixing the algorithm keyword with keX_ (X being
1..7), e.g. 'x25519-ke1_mlkem768'.

The 'dh_group' option only allows a single key exchange method. Add a
'ke' list option to the crypto_proposal sections, which holds the
additional key exchange methods. Both config_ike_proposal() and
config_esp_proposal() append them to the generated proposal after
dh_group, so 'x25519' plus 'list ke mlkem768' results in
'x25519-ke1_mlkem768'.

The keN_ prefix is generated by the init script from the position of
the entry in the list. Entries which already carry a keN_ prefix are
used verbatim with a warning, which keeps keX_none (used to make a
key exchange round optional) working. Entries beyond the seventh are
dropped with a warning. A warning is also emitted if key exchange
methods are configured without a dh_group, since the first key
exchange method is mandatory.

Signed-off-by: Florian Eckert <fe@dev.tdt.de>
---
 net/strongswan/files/swanctl.init | 42 +++++++++++++++++++++++++++++--
 1 file changed, 40 insertions(+), 2 deletions(-)

diff --git a/net/strongswan/files/swanctl.init b/net/strongswan/files/swanctl.init
index fa82e09c15..e39656c02b 100644
--- a/net/strongswan/files/swanctl.init
+++ b/net/strongswan/files/swanctl.init
@@ -154,6 +154,26 @@ is_aead() {
 	return 1
 }
 
+append_ke() {
+	local value="$1"
+
+	[ -n "$value" ] || return
+
+	ke_count="$((ke_count + 1))"
+	[ "$ke_count" -le 7 ] || {
+		warning "More than 7 key exchange methods configured, ignoring '$value'"
+		return
+	}
+
+	case "$value" in
+	ke[1-7]_*)
+		warning "Key exchange method '$value' already has a keN_ prefix, using it verbatim"
+		ke="$ke-$value" ;;
+	*)
+		ke="$ke-ke${ke_count}_${value}" ;;
+	esac
+}
+
 config_esp_proposal() {
 	local conf="$1"
 
@@ -161,6 +181,8 @@ config_esp_proposal() {
 	local encryption_algorithm
 	local hash_algorithm
 	local dh_group
+	local ke
+	local ke_count
 
 	config_get_bool use_custom_proposal "$conf" use_custom_proposal 0
 	[ "$use_custom_proposal" = "1" ] && {
@@ -177,14 +199,21 @@ config_esp_proposal() {
 	config_get hash_algorithm "$conf" hash_algorithm
 	config_get dh_group "$conf" dh_group
 
+	ke=""
+	ke_count=0
+	config_list_foreach "$conf" ke append_ke
+
 	# check for AEAD and clobber hash_algorithm if set
 	if is_aead "$encryption_algorithm" && [ -n "$hash_algorithm" ]; then
 		fatal "Can't have $hash_algorithm with $encryption_algorithm"
 		hash_algorithm=
 	fi
 
+	[ -n "$ke" ] && [ -z "$dh_group" ] && \
+		warning "Key exchange methods in '$conf' require a dh_group"
+
 	[ -n "$encryption_algorithm" ] && \
-		crypto="${crypto:+${crypto},}${encryption_algorithm}${hash_algorithm:+-${hash_algorithm}}${dh_group:+-${dh_group}}"
+		crypto="${crypto:+${crypto},}${encryption_algorithm}${hash_algorithm:+-${hash_algorithm}}${dh_group:+-${dh_group}}${ke}"
 }
 
 iter_esp_proposal() {
@@ -206,6 +235,8 @@ config_ike_proposal() {
 	local hash_algorithm
 	local dh_group
 	local prf_algorithm
+	local ke
+	local ke_count
 
 	config_get_bool use_custom_proposal "$conf" use_custom_proposal 0
 	[ "$use_custom_proposal" = "1" ] && {
@@ -223,14 +254,21 @@ config_ike_proposal() {
 	config_get dh_group "$conf" dh_group
 	config_get prf_algorithm "$conf" prf_algorithm
 
+	ke=""
+	ke_count=0
+	config_list_foreach "$conf" ke append_ke
+
 	# check for AEAD and clobber hash_algorithm if set
 	if is_aead "$encryption_algorithm" && [ -n "$hash_algorithm" ]; then
 		fatal "Can't have $hash_algorithm with $encryption_algorithm"
 		hash_algorithm=
 	fi
 
+	[ -n "$ke" ] && [ -z "$dh_group" ] && \
+		warning "Key exchange methods in '$conf' require a dh_group"
+
 	[ -n "$encryption_algorithm" ] && \
-		crypto="${crypto:+${crypto},}${encryption_algorithm}${hash_algorithm:+-${hash_algorithm}}${prf_algorithm:+-${prf_algorithm}}${dh_group:+-${dh_group}}"
+		crypto="${crypto:+${crypto},}${encryption_algorithm}${hash_algorithm:+-${hash_algorithm}}${prf_algorithm:+-${prf_algorithm}}${dh_group:+-${dh_group}}${ke}"
 }
 
 iter_ike_proposal() {