[Root] IPv6 is not resolved within IPv6 VPNs if main connection is IPv4-only

[ameshkov]

It looks as if after adding the iptables rules system DNS no more responds to the AAAA requests. I've no idea why yet.
adguard (5).log
adguard (4).log

"androidVersion" : "7.1.2 (sdk=25)",
"deviceName" : "manufacturer=Xiaomi model=Redmi Note 3 brand=Xiaomi version=7.1.2 security_patch=2018-07-05",

[ameshkov]

Also, user reports that it does work on AG v2.11

[ameshkov]

@sfionov could you please check the logs and see if there are anything suspicious?

[sfionov]

@ameshkov We auto-detect lack of IPv6 during DnsUpstream setup. That's not very good if system doesn't have IPv6 but VPNs do.

[ameshkov]

The problem is that IPv6 does not work even when DNS filtering is disabled

[sfionov]

Java makes getaddrinfo requests using AI_ADDRCONFIG flag (check ipv6/ipv4 availability before request), but _have_ipv6 for AI_ADDRCONFIG checks that interface has address from 2000::/3 global unicast:
https://android.googlesource.com/platform/bionic/+/oreo-release/libc/dns/net/getaddrinfo.c#370
ULA addresses from fc00::/7 are not checked there.
I wonder why it works without us

[sfionov]

Sorry, I've read the code not carefully enough. That check is about availability of 2000:: address via UDP.
I've look this more closely.

[sfionov]

The main problem is that VPN have IPv6 but system doesn't.
We may fix it for DnsUpstream, but can't fix it for system getaddrinfo cache.

[sfionov]

The main problem is that NetworkUtils.hasIPv6Network() (used in DnsUpstream) ignores VPN interfaces.
That is good idea if we are VPN, but breaks IPv6 in VPNs in root mode.
So, we need to exclude VPNs in that check only if filteringMode is VPN.