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(a)gibson.dropbear.id.au> --- 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