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
---
fwd.c | 18 ++++++++++++++++--
1 file changed, 16 insertions(+), 2 deletions(-)
diff --git a/fwd.c b/fwd.c
index bd16ac42..3f864f85 100644
--- a/fwd.c
+++ b/fwd.c
@@ -156,6 +156,20 @@ 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
@@ -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)) {
--
2.45.2