Although it's not 100% explicit in the man page, addresses given to the
--dns option are intended to be addresses as seen by the guest. This
differs from addresses taken from the host's /etc/resolv.conf, which must
be translated to to guest accessible versions in some cases.
Our implementation is currently inconsistent on this: when using
--dns-forward, you must usually also give --dns with the matching address,
which is meaningful only in the guest's address view. However if you give
--dns with a loopback addres, it will be translated like a host view
address.
Move the remapping logic for DNS addresses out of add_dns4() and add_dns6()
into add_dns_resolv() so that it is only applied for host nameserver
addresses, not for nameservers given explicitly with --dns.
Signed-off-by: David Gibson <david(a)gibson.dropbear.id.au>
---
conf.c | 88 ++++++++++++++++++++++++++++-----------------------------
passt.1 | 14 +++++----
2 files changed, 52 insertions(+), 50 deletions(-)
diff --git a/conf.c b/conf.c
index bf61c143..3c102bcf 100644
--- a/conf.c
+++ b/conf.c
@@ -353,7 +353,7 @@ bind_all_fail:
/**
* add_dns4() - Possibly add the IPv4 address of a DNS resolver to configuration
* @c: Execution context
- * @addr: Address found in /etc/resolv.conf
+ * @addr: Guest nameserver IPv4 address
* @idx: Index of free entry in array of IPv4 resolvers
*
* Return: Number of entries added (0 or 1)
@@ -361,64 +361,29 @@ bind_all_fail:
static unsigned add_dns4(struct ctx *c, const struct in_addr *addr,
unsigned idx)
{
- unsigned added = 0;
-
if (idx >= ARRAY_SIZE(c->ip4.dns))
return 0;
- /* Guest or container can only access local addresses via redirect */
- if (IN4_IS_ADDR_LOOPBACK(addr)) {
- if (!c->no_map_gw) {
- c->ip4.dns[idx] = c->ip4.gw;
- added++;
-
- if (IN4_IS_ADDR_UNSPECIFIED(&c->ip4.dns_match))
- c->ip4.dns_match = c->ip4.gw;
- }
- } else {
- c->ip4.dns[idx] = *addr;
- added++;
- }
-
- if (IN4_IS_ADDR_UNSPECIFIED(&c->ip4.dns_host))
- c->ip4.dns_host = *addr;
-
- return added;
+ c->ip4.dns[idx] = *addr;
+ return 1;
}
/**
* add_dns6() - Possibly add the IPv6 address of a DNS resolver to configuration
* @c: Execution context
- * @addr: Address found in /etc/resolv.conf
+ * @addr: Guest nameserver IPv6 address
* @idx: Index of free entry in array of IPv6 resolvers
*
* Return: Number of entries added (0 or 1)
*/
-static unsigned add_dns6(struct ctx *c, struct in6_addr *addr, unsigned idx)
+static unsigned add_dns6(struct ctx *c, const struct in6_addr *addr,
+ unsigned idx)
{
- unsigned added = 0;
-
if (idx >= ARRAY_SIZE(c->ip6.dns))
return 0;
- /* Guest or container can only access local addresses via redirect */
- if (IN6_IS_ADDR_LOOPBACK(addr)) {
- if (!c->no_map_gw) {
- c->ip6.dns[idx] = c->ip6.gw;
- added++;
-
- if (IN6_IS_ADDR_UNSPECIFIED(&c->ip6.dns_match))
- c->ip6.dns_match = c->ip6.gw;
- }
- } else {
- c->ip6.dns[idx] = *addr;
- added++;
- }
-
- if (IN6_IS_ADDR_UNSPECIFIED(&c->ip6.dns_host))
- c->ip6.dns_host = *addr;
-
- return added;
+ c->ip6.dns[idx] = *addr;
+ return 1;
}
/**
@@ -437,11 +402,44 @@ static void add_dns_resolv(struct ctx *c, const char *nameserver,
struct in6_addr ns6;
struct in_addr ns4;
- if (idx4 && inet_pton(AF_INET, nameserver, &ns4))
+ if (idx4 && inet_pton(AF_INET, nameserver, &ns4)) {
+ if (IN4_IS_ADDR_UNSPECIFIED(&c->ip4.dns_host))
+ c->ip4.dns_host = ns4;
+
+ /* Guest or container can only access local addresses via
+ * redirect
+ */
+ if (IN4_IS_ADDR_LOOPBACK(&ns4)) {
+ if (c->no_map_gw)
+ return;
+
+ ns4 = c->ip4.gw;
+ if (IN4_IS_ADDR_UNSPECIFIED(&c->ip4.dns_match))
+ c->ip4.dns_match = c->ip4.gw;
+ }
+
*idx4 += add_dns4(c, &ns4, *idx4);
+ }
+
+ if (idx6 && inet_pton(AF_INET6, nameserver, &ns6)) {
+ if (IN6_IS_ADDR_UNSPECIFIED(&c->ip6.dns_host))
+ c->ip6.dns_host = ns6;
+
+ /* Guest or container can only access local addresses via
+ * redirect
+ */
+ if (IN6_IS_ADDR_LOOPBACK(&ns6)) {
+ if (c->no_map_gw)
+ return;
+
+ ns6 = c->ip6.gw;
+
+ if (IN6_IS_ADDR_UNSPECIFIED(&c->ip6.dns_match))
+ c->ip6.dns_match = c->ip6.gw;
+ }
- if (idx6 && inet_pton(AF_INET6, nameserver, &ns6))
*idx6 += add_dns6(c, &ns6, *idx6);
+ }
}
/**
diff --git a/passt.1 b/passt.1
index 3062b719..dca433b6 100644
--- a/passt.1
+++ b/passt.1
@@ -236,11 +236,15 @@ interface will be chosen instead.
.TP
.BR \-D ", " \-\-dns " " \fIaddr
-Use \fIaddr\fR (IPv4 or IPv6) for DHCP, DHCPv6, NDP or DNS forwarding, as
-configured (see options \fB--no-dhcp-dns\fR, \fB--dhcp-dns\fR,
-\fB--dns-forward\fR) instead of reading addresses from \fI/etc/resolv.conf\fR.
-This option can be specified multiple times. Specifying \fB-D none\fR disables
-usage of DNS addresses altogether.
+Instruct the guest (via DHCP, DHVPv6 or NDP) to use \fIaddr\fR (IPv4
+or IPv6) as a nameserver, as configured (see options
+\fB--no-dhcp-dns\fR, \fB--dhcp-dns\fR) instead of reading addresses
+from \fI/etc/resolv.conf\fR. This option can be specified multiple
+times. Specifying \fB-D none\fR disables usage of DNS addresses
+altogether. Unlike addresses from \fI/etc/resolv.conf\fR, \fIaddr\fR
+is given to the guest without remapping. For example \fB--dns
+127.0.0.1\fR will instruct the guest to use itself as nameserver, not
+the host.
.TP
.BR \-\-dns-forward " " \fIaddr
--
2.46.0