From becf81ab888aeb8fd682b572576f257ab9e9e96f Mon Sep 17 00:00:00 2001 From: David Gibson Date: Wed, 24 Jul 2024 17:51:12 +1000 Subject: [PATCH] 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 Tested-by: Paul Holzinger Signed-off-by: Stefano Brivio --- fwd.c | 18 ++++++++++++++++-- passt.1 | 10 +++++----- 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 @@ -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)) 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