wg: give "off" value for fwmark

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

src/config.c

@@ -97,6 +97,12 @@ static inline bool parse_fwmark(uint32_t *fwmark, unsigned int *flags, const cha
 	char *end;
 	int base = 10;
 
+	if (!strcasecmp(value, "off")) {
+		*fwmark = 0;
+		*flags |= WGDEVICE_REMOVE_FWMARK;
+		return true;
+	}
+
 	if (value[0] == '0' && value[1] == 'x') {
 		value += 2;
 		base = 16;

src/show.c

@@ -276,7 +276,10 @@ static bool ugly_print(struct wgdevice *device, const char *param, bool with_int
 	} else if (!strcmp(param, "fwmark")) {
 		if (with_interface)
 			printf("%s\t", device->interface);
+		if (device->fwmark)
 			printf("0x%x\n", device->fwmark);
+		else
+			printf("off\n");
 	} else if (!strcmp(param, "endpoints")) {
 		if (with_interface)
 			printf("%s\t", device->interface);

src/wg-quick.bash

@@ -79,7 +79,9 @@ add_if() {
 }
 
 del_if() {
-	DEFAULT_TABLE=$(( $(wg show "$INTERFACE" fwmark) ))
+	local fwmark="$(wg show "$INTERFACE" fwmark)"
+	DEFAULT_TABLE=0
+	[[ $fwmark != off ]] && DEFAULT_TABLE=$(( $fwmark ))
 	if [[ $DEFAULT_TABLE -ne 0 ]]; then
 		while [[ -n $(ip -4 rule show table $DEFAULT_TABLE) ]]; do
 			cmd ip -4 rule delete table $DEFAULT_TABLE

src/wg.8

@@ -67,14 +67,16 @@ it adds an additional layer of symmetric-key cryptography to be mixed into
 the already existing public-key cryptography, for post-quantum resistance.
 If \fIallowed-ips\fP is specified, but the value is the empty string, all
 allowed ips are removed from the peer. The use of \fIpersistent-keepalive\fP
-is optional and is by default off; setting it to 0 or "off", disables it.
+is optional and is by default off; setting it to 0 or "off" disables it.
 Otherwise it represents, in seconds, between 1 and 65535 inclusive, how often
 to send an authenticated empty packet to the peer, for the purpose of keeping
 a stateful firewall or NAT mapping valid persistently. For example, if the
 interface very rarely sends traffic, but it might at anytime receive traffic
 from a peer, and it is behind NAT, the interface might benefit from having a
 persistent keepalive interval of 25 seconds; however, most users will not need
-this.
+this. The use of \fIfwmark\fP is optional and is by default off; setting it to
+0 or "off" disables it. Otherwise it is a 32-bit fwmark for outgoing packets
+and may be specified in hexadecimal by prepending "0x".
 .TP
 \fBsetconf\fP \fI<interface>\fP \fI<configuration-filename>\fP
 Sets the current configuration of \fI<interface>\fP to the contents of
@@ -126,7 +128,8 @@ for post-quantum resistance.
 ListenPort \(em a 16-bit port for listening. Optional; if not specified, chosen
 randomly.
 .IP \(bu
-FwMark \(em a 32-bit fwmark for outgoing packets. Optional.
+FwMark \(em a 32-bit fwmark for outgoing packets. If set to 0 or "off", this
+option is disabled. May be specified in hexadecimal by prepending "0x". Optional.
 .P
 The \fIPeer\fP sections may contain the following fields:
 .IP \(bu