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authorDavid Gibson <david@gibson.dropbear.id.au>2024-07-24 17:51:12 +1000
committerStefano Brivio <sbrivio@redhat.com>2024-07-25 12:38:11 +0200
commitbecf81ab888aeb8fd682b572576f257ab9e9e96f (patch)
tree06150a41046ec157aa60ac813a71d2717a19ad0f
parent0ada84e3f8c5e76d47725f45082f012a56efe433 (diff)
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fwd: Broaden what we consider for DNS specific forwarding rules
passt/pasta has options to redirect DNS requests from the guest to a different server address on the host side. Currently, however, only UDP packets to port 53 are considered "DNS requests". This ignores DNS requests over TCP - less common, but certainly possible. It also ignores encrypted DNS requests on port 853. Extend the DNS forwarding logic to handle both of those cases. Link: https://github.com/containers/podman/issues/23239 Signed-off-by: David Gibson <david@gibson.dropbear.id.au> Tested-by: Paul Holzinger <pholzing@redhat.com> Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
-rw-r--r--fwd.c18
-rw-r--r--passt.110
2 files changed, 21 insertions, 7 deletions
diff --git a/fwd.c b/fwd.c
index c323aba..dea36f6 100644
--- a/fwd.c
+++ b/fwd.c
@@ -157,6 +157,20 @@ void fwd_scan_ports_init(struct ctx *c)
}
/**
+ * is_dns_flow() - Determine if flow appears to be a DNS request
+ * @proto: Protocol (IP L4 protocol number)
+ * @ini: Flow address information of the initiating side
+ *
+ * Return: true if the flow appears to be directed at a dns server, that is a
+ * TCP or UDP flow to port 53 (domain) or port 853 (domain-s)
+ */
+static bool is_dns_flow(uint8_t proto, const struct flowside *ini)
+{
+ return ((proto == IPPROTO_UDP) || (proto == IPPROTO_TCP)) &&
+ ((ini->fport == 53) || (ini->fport == 853));
+}
+
+/**
* fwd_nat_from_tap() - Determine to forward a flow from the tap interface
* @c: Execution context
* @proto: Protocol (IP L4 protocol number)
@@ -169,10 +183,10 @@ void fwd_scan_ports_init(struct ctx *c)
uint8_t fwd_nat_from_tap(const struct ctx *c, uint8_t proto,
const struct flowside *ini, struct flowside *tgt)
{
- if (proto == IPPROTO_UDP && ini->fport == 53 &&
+ if (is_dns_flow(proto, ini) &&
inany_equals4(&ini->faddr, &c->ip4.dns_match))
tgt->eaddr = inany_from_v4(c->ip4.dns_host);
- else if (proto == IPPROTO_UDP && ini->fport == 53 &&
+ else if (is_dns_flow(proto, ini) &&
inany_equals6(&ini->faddr, &c->ip6.dns_match))
tgt->eaddr.a6 = c->ip6.dns_host;
else if (!c->no_map_gw && inany_equals4(&ini->faddr, &c->ip4.gw))
diff --git a/passt.1 b/passt.1
index abc13d5..81789cc 100644
--- a/passt.1
+++ b/passt.1
@@ -244,11 +244,11 @@ usage of DNS addresses altogether.
.TP
.BR \-\-dns-forward " " \fIaddr
-Map \fIaddr\fR (IPv4 or IPv6) as seen from guest or namespace to the first
-configured DNS resolver (with corresponding IP version). Mapping is limited to
-UDP traffic directed to port 53, and DNS answers are translated back with a
-reverse mapping.
-This option can be specified zero to two times (once for IPv4, once for IPv6).
+Map \fIaddr\fR (IPv4 or IPv6) as seen from guest or namespace to the
+first configured DNS resolver (with corresponding IP version). Maps
+only UDP and TCP traffic to port 53 or port 853. Replies are
+translated back with a reverse mapping. This option can be specified
+zero to two times (once for IPv4, once for IPv6).
.TP
.BR \-S ", " \-\-search " " \fIlist