[ebtables-compat PATCH 4/7] ebtables-compat: prevent same matches to be included multiple times

[Arturo Borrero Gonzalez <arturo.borrero.glez@gmail.com>]

Using two matches options results in two copies of the match being included
in the nft rule.

Example before this patch:
 % ebtables-compat -A FORWARD -p 0x0800 --ip-src 10.0.0.1 --ip-dst 10.0.0.2 -j ACCEPT
 % ebtables-compat -L
 [...]
 -p 0x0800 --ip-src 10.0.0.1 --ip-dst 10.0.0.2 --ip-src 10.0.0.1 --ip-dst 10.0.0.2 -j ACCEPT

Example with this patch:
 % ebtables-compat -A FORWARD -p 0x0800 --ip-src 10.0.0.1 --ip-dst 10.0.0.2 -j ACCEPT
 % ebtables-compat -L
 [...]
 % -p 0x0800 --ip-src 10.0.0.1 --ip-dst 10.0.0.2 -j ACCEPT

[Note: the br_ip extension comes in a follow-up patch]

Signed-off-by: Arturo Borrero Gonzalez <arturo.borrero.glez@gmail.com>
---
 iptables/xtables-eb.c |    8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/iptables/xtables-eb.c b/iptables/xtables-eb.c
index b559a53..a078679 100644
--- a/iptables/xtables-eb.c
+++ b/iptables/xtables-eb.c
@@ -644,6 +644,14 @@ static void ebt_load_matches(void)
 static void ebt_add_match(struct xtables_match *m,
 			  struct xtables_rule_match **rule_matches)
 {
+	struct xtables_rule_match *i;
+
+	/* match already in rule_matches, skip inclusion */
+	for (i = *rule_matches; i; i = i->next) {
+		if (strcmp(m->name, i->match->name) == 0)
+			return;
+	}
+
 	if (xtables_find_match(m->name, XTF_LOAD_MUST_SUCCEED, rule_matches) == NULL)
 		xtables_error(OTHER_PROBLEM,
 			      "Unable to add match %s", m->name);