From 89678c515755403277938e34984f3faf4863d593 Mon Sep 17 00:00:00 2001 From: Stefano Brivio Date: Fri, 18 Feb 2022 04:03:53 +0100 Subject: conf, udp: Introduce basic DNS forwarding For compatibility with libslirp/slirp4netns users: introduce a mechanism to map, in the UDP routines, an address facing guest or namespace to the first IPv4 or IPv6 address resulting from configuration as resolver. This can be enabled with the new --dns-forward option. This implies that sourcing and using DNS addresses and search lists, passed via command line or read from /etc/resolv.conf, is not bound anymore to DHCP/DHCPv6/NDP usage: for example, pasta users might just want to use addresses from /etc/resolv.conf as mapping target, while not passing DNS options via DHCP. Reflect this in all the involved code paths by differentiating DHCP/DHCPv6/NDP usage from DNS configuration per se, and in the new options --dhcp-dns, --dhcp-search for pasta, and --no-dhcp-dns, --no-dhcp-search for passt. This should be the last bit to enable substantial compatibility between slirp4netns.sh and slirp4netns(1): pass the --dns-forward option from the script too. Signed-off-by: Stefano Brivio --- ndp.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) (limited to 'ndp.c') diff --git a/ndp.c b/ndp.c index 386098c..6b1c1a8 100644 --- a/ndp.c +++ b/ndp.c @@ -127,6 +127,9 @@ int ndp(struct ctx *c, struct ethhdr *eh, size_t len) p += 4; } + if (c->no_dhcp_dns) + goto dns_done; + for (n = 0; !IN6_IS_ADDR_UNSPECIFIED(&c->dns6[n]); n++); if (n) { *p++ = 25; /* RDNSS */ @@ -144,7 +147,7 @@ int ndp(struct ctx *c, struct ethhdr *eh, size_t len) dns_s_len += strlen(c->dns_search[n].n) + 2; } - if (dns_s_len) { + if (!c->no_dhcp_dns_search && dns_s_len) { *p++ = 31; /* DNSSL */ *p++ = (len + 8 - 1) / 8 + 1; /* length */ p += 2; /* reserved */ @@ -171,6 +174,7 @@ int ndp(struct ctx *c, struct ethhdr *eh, size_t len) p += 8 - dns_s_len % 8; } +dns_done: *p++ = 1; /* source ll */ *p++ = 1; /* length */ memcpy(p, c->mac, ETH_ALEN); -- cgit v1.2.3