From 10583537004f7ecd4aa11f6c12b7ba73fb77fc11 Mon Sep 17 00:00:00 2001
From: Phil Sutter <phil@nwl.cc>
Date: Fri, 21 Jul 2023 13:14:36 +0200
Subject: nft: Special casing for among match in compare_matches()

When other extensions may have "garbage" appended to their data which
should not be considered for match comparison, among match is the
opposite in that it extends its data beyond the value in 'size' field.
Add special casing to cover for this, avoiding false-positive rule
comparison.

Fixes: 26753888720d8 ("nft: bridge: Rudimental among extension support")
Signed-off-by: Phil Sutter <phil@nwl.cc>

Conflict:NA
Reference:https://git.netfilter.org/iptables//commit/?id=10583537004f7ecd4aa11f6c12b7ba73fb77fc11

---
 iptables/nft-shared.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/iptables/nft-shared.c b/iptables/nft-shared.c
index 10553ab..4c20ceb 100644
--- a/iptables/nft-shared.c
+++ b/iptables/nft-shared.c
@@ -933,6 +933,7 @@ bool compare_matches(struct xtables_rule_match *mt1,
 	for (mp1 = mt1, mp2 = mt2; mp1 && mp2; mp1 = mp1->next, mp2 = mp2->next) {
 		struct xt_entry_match *m1 = mp1->match->m;
 		struct xt_entry_match *m2 = mp2->match->m;
+		size_t cmplen = mp1->match->userspacesize;
 
 		if (strcmp(m1->u.user.name, m2->u.user.name) != 0) {
 			DEBUGP("mismatching match name\n");
@@ -944,8 +945,10 @@ bool compare_matches(struct xtables_rule_match *mt1,
 			return false;
 		}
 
-		if (memcmp(m1->data, m2->data,
-			   mp1->match->userspacesize) != 0) {
+		if (!strcmp(m1->u.user.name, "among"))
+			cmplen = m1->u.match_size - sizeof(*m1);
+
+		if (memcmp(m1->data, m2->data, cmplen) != 0) {
 			DEBUGP("mismatch match data\n");
 			return false;
 		}
-- 
2.33.0