[PATCH] arp: only send ARP replies for --gateway address

[Nikolay Edigaryev <edigaryev@gmail.com>]

Problem: when passt/pasta are working in a broadcast domain with more
than one host machine, it will answer for all of these machines,
except for the one having --address. This is akin to ARP spoofing
and breaks connection with these machines if passt/pasta ARP reply
arrives before the original one.

Solution: only be responsible and send ARP replies
for the --gateway's address.
---
 arp.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arp.c b/arp.c
index a35c1b6..f873491 100644
--- a/arp.c
+++ b/arp.c
@@ -67,8 +67,8 @@ int arp(const struct ctx *c, const struct pool *p)
 	    !memcmp(am->sip, am->tip, sizeof(am->sip)))
 		return 1;
 
-	/* Don't resolve our own address, either. */
-	if (!memcmp(am->tip, &c->ip4.addr, sizeof(am->tip)))
+	/* Don't resolve anything but gateway address. */
+	if (memcmp(am->tip, &c->ip4.gw, sizeof(am->tip)) != 0)
 		return 1;
 
 	ah->ar_op = htons(ARPOP_REPLY);
-- 
@@ -67,8 +67,8 @@ int arp(const struct ctx *c, const struct pool *p)
 	    !memcmp(am->sip, am->tip, sizeof(am->sip)))
 		return 1;
 
-	/* Don't resolve our own address, either. */
-	if (!memcmp(am->tip, &c->ip4.addr, sizeof(am->tip)))
+	/* Don't resolve anything but gateway address. */
+	if (memcmp(am->tip, &c->ip4.gw, sizeof(am->tip)) != 0)
 		return 1;
 
 	ah->ar_op = htons(ARPOP_REPLY);
-- 
2.39.2 (Apple Git-144)