[PATCH 3/3] udp: Check for answers to forwarded DNS queries before handling local redirects

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From: Stefano Brivio <sbrivio@redhat.com>
To: passt-dev@passt.top
Cc: Paul Holzinger <pholzing@redhat.com>,
	David Gibson <david@gibson.dropbear.id.au>
Subject: [PATCH 3/3] udp: Check for answers to forwarded DNS queries before handling local redirects
Date: Thu,  3 Nov 2022 00:04:43 +0100	[thread overview]
Message-ID: <20221102230443.377446-4-sbrivio@redhat.com> (raw)
In-Reply-To: <20221102230443.377446-1-sbrivio@redhat.com>

Now that we allow loopback DNS addresses to be used as targets for
forwarding, we need to check if DNS answers come from those targets,
before deciding to eventually remap traffic for local redirects.

Otherwise, the source address won't match the one configured as
forwarder, which means that the guest or the container will refuse
those responses.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
---
 udp.c | 17 ++++++++---------
 1 file changed, 8 insertions(+), 9 deletions(-)

diff --git a/udp.c b/udp.c
index 4b201d3..7c77e09 100644
--- a/udp.c
+++ b/udp.c
@@ -680,8 +680,10 @@ static void udp_sock_fill_data_v4(const struct ctx *c, int n,
 	src = ntohl(b->s_in.sin_addr.s_addr);
 	src_port = ntohs(b->s_in.sin_port);
 
-	if (src >> IN_CLASSA_NSHIFT == IN_LOOPBACKNET ||
-	    src == INADDR_ANY || src == ntohl(c->ip4.addr_seen)) {
+	if (c->ip4.dns_fwd && src == htonl(c->ip4.dns[0]) && src_port == 53) {
+		b->iph.saddr = c->ip4.dns_fwd;
+	} else if (IPV4_IS_LOOPBACK(src) || src == INADDR_ANY ||
+		   src == ntohl(c->ip4.addr_seen)) {
 		b->iph.saddr = c->ip4.gw;
 		udp_tap_map[V4][src_port].ts = now->tv_sec;
 		udp_tap_map[V4][src_port].flags |= PORT_LOCAL;
@@ -692,9 +694,6 @@ static void udp_sock_fill_data_v4(const struct ctx *c, int n,
 			udp_tap_map[V4][src_port].flags |= PORT_LOOPBACK;
 
 		bitmap_set(udp_act[V4][UDP_ACT_TAP], src_port);
-	} else if (c->ip4.dns_fwd &&
-		   src == htonl(c->ip4.dns[0]) && src_port == 53) {
-		b->iph.saddr = c->ip4.dns_fwd;
 	} else {
 		b->iph.saddr = b->s_in.sin_addr.s_addr;
 	}
@@ -770,6 +769,10 @@ static void udp_sock_fill_data_v6(const struct ctx *c, int n,
 	if (IN6_IS_ADDR_LINKLOCAL(src)) {
 		b->ip6h.daddr = c->ip6.addr_ll_seen;
 		b->ip6h.saddr = b->s_in6.sin6_addr;
+	} else if (!IN6_IS_ADDR_UNSPECIFIED(&c->ip6.dns_fwd) &&
+		   IN6_ARE_ADDR_EQUAL(src, &c->ip6.dns[0]) && src_port == 53) {
+		b->ip6h.daddr = c->ip6.addr_seen;
+		b->ip6h.saddr = c->ip6.dns_fwd;
 	} else if (IN6_IS_ADDR_LOOPBACK(src)			||
 		   IN6_ARE_ADDR_EQUAL(src, &c->ip6.addr_seen)	||
 		   IN6_ARE_ADDR_EQUAL(src, &c->ip6.addr)) {
@@ -794,10 +797,6 @@ static void udp_sock_fill_data_v6(const struct ctx *c, int n,
 			udp_tap_map[V6][src_port].flags &= ~PORT_GUA;
 
 		bitmap_set(udp_act[V6][UDP_ACT_TAP], src_port);
-	} else if (!IN6_IS_ADDR_UNSPECIFIED(&c->ip6.dns_fwd) &&
-		   IN6_ARE_ADDR_EQUAL(src, &c->ip6.dns[0]) && src_port == 53) {
-		b->ip6h.daddr = c->ip6.addr_seen;
-		b->ip6h.saddr = c->ip6.dns_fwd;
 	} else {
 		b->ip6h.daddr = c->ip6.addr_seen;
 		b->ip6h.saddr = b->s_in6.sin6_addr;
-- 
@@ -680,8 +680,10 @@ static void udp_sock_fill_data_v4(const struct ctx *c, int n,
 	src = ntohl(b->s_in.sin_addr.s_addr);
 	src_port = ntohs(b->s_in.sin_port);
 
-	if (src >> IN_CLASSA_NSHIFT == IN_LOOPBACKNET ||
-	    src == INADDR_ANY || src == ntohl(c->ip4.addr_seen)) {
+	if (c->ip4.dns_fwd && src == htonl(c->ip4.dns[0]) && src_port == 53) {
+		b->iph.saddr = c->ip4.dns_fwd;
+	} else if (IPV4_IS_LOOPBACK(src) || src == INADDR_ANY ||
+		   src == ntohl(c->ip4.addr_seen)) {
 		b->iph.saddr = c->ip4.gw;
 		udp_tap_map[V4][src_port].ts = now->tv_sec;
 		udp_tap_map[V4][src_port].flags |= PORT_LOCAL;
@@ -692,9 +694,6 @@ static void udp_sock_fill_data_v4(const struct ctx *c, int n,
 			udp_tap_map[V4][src_port].flags |= PORT_LOOPBACK;
 
 		bitmap_set(udp_act[V4][UDP_ACT_TAP], src_port);
-	} else if (c->ip4.dns_fwd &&
-		   src == htonl(c->ip4.dns[0]) && src_port == 53) {
-		b->iph.saddr = c->ip4.dns_fwd;
 	} else {
 		b->iph.saddr = b->s_in.sin_addr.s_addr;
 	}
@@ -770,6 +769,10 @@ static void udp_sock_fill_data_v6(const struct ctx *c, int n,
 	if (IN6_IS_ADDR_LINKLOCAL(src)) {
 		b->ip6h.daddr = c->ip6.addr_ll_seen;
 		b->ip6h.saddr = b->s_in6.sin6_addr;
+	} else if (!IN6_IS_ADDR_UNSPECIFIED(&c->ip6.dns_fwd) &&
+		   IN6_ARE_ADDR_EQUAL(src, &c->ip6.dns[0]) && src_port == 53) {
+		b->ip6h.daddr = c->ip6.addr_seen;
+		b->ip6h.saddr = c->ip6.dns_fwd;
 	} else if (IN6_IS_ADDR_LOOPBACK(src)			||
 		   IN6_ARE_ADDR_EQUAL(src, &c->ip6.addr_seen)	||
 		   IN6_ARE_ADDR_EQUAL(src, &c->ip6.addr)) {
@@ -794,10 +797,6 @@ static void udp_sock_fill_data_v6(const struct ctx *c, int n,
 			udp_tap_map[V6][src_port].flags &= ~PORT_GUA;
 
 		bitmap_set(udp_act[V6][UDP_ACT_TAP], src_port);
-	} else if (!IN6_IS_ADDR_UNSPECIFIED(&c->ip6.dns_fwd) &&
-		   IN6_ARE_ADDR_EQUAL(src, &c->ip6.dns[0]) && src_port == 53) {
-		b->ip6h.daddr = c->ip6.addr_seen;
-		b->ip6h.saddr = c->ip6.dns_fwd;
 	} else {
 		b->ip6h.daddr = c->ip6.addr_seen;
 		b->ip6h.saddr = b->s_in6.sin6_addr;
-- 
2.35.1

next prev parent reply	other threads:[~2022-11-02 23:04 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-11-02 23:04 [PATCH 0/3] Fixes and workarounds for pasta with Podman in Google Cloud Stefano Brivio
2022-11-02 23:04 ` [PATCH 1/3] conf: Consistency check between configured IPv4 netmask and gateway Stefano Brivio
2022-11-03  3:17   ` David Gibson
2022-11-03  6:39     ` Stefano Brivio
2022-11-02 23:04 ` [PATCH 2/3] conf: Split the notions of read DNS addresses and offered ones Stefano Brivio
2022-11-03  3:37   ` David Gibson
2022-11-03  6:42     ` Stefano Brivio
2022-11-02 23:04 ` Stefano Brivio [this message]
2022-11-03  3:42   ` [PATCH 3/3] udp: Check for answers to forwarded DNS queries before handling local redirects David Gibson
2022-11-03  6:42     ` Stefano Brivio
2022-11-05  1:19       ` David Gibson
2022-11-06 22:22         ` Stefano Brivio
2022-11-07  1:08           ` David Gibson
2022-11-07  9:51             ` Stefano Brivio
2022-11-08  5:51               ` David Gibson
2022-11-08  6:22                 ` Stefano Brivio
2022-11-10  4:30                   ` David Gibson
2022-11-03  3:13 ` [PATCH 0/3] Fixes and workarounds for pasta with Podman in Google Cloud David Gibson
2022-11-03  6:36   ` Stefano Brivio

find likely ancestor, descendant, or conflicting patches for this message:
dfblob:4b201d3 dfblob:7c77e09
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