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net/dnscache: Handle 4-in-6 addresses in DNS responses

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On Android, the system resolver can return IPv4 addresses as IPv6-mapped
addresses (i.e. `::ffff:a.b.c.d`). After the switch to `net/netip`
(19008a3), this case is no longer handled and a response like this will
be seen as failure to resolve any IPv4 addresses.

Handle this case by simply calling `Unmap()` on the returned IPs. Fixes #5698.

Signed-off-by: Peter Cai <peter@typeblog.net>
This commit is contained in:
Peter Cai 2022-10-22 15:55:59 -04:00 committed by Brad Fitzpatrick
parent 70dde89c34
commit 4597ec1037
1 changed files with 5 additions and 0 deletions
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5
net/dnscache/dnscache.go
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@ -276,6 +276,11 @@ func (r *Resolver) lookupIP(host string) (ip, ip6 netip.Addr, allIPs []netip.Add
return netip.Addr{}, netip.Addr{}, nil, fmt.Errorf("no IPs for %q found", host)
}
// Unmap everything; LookupNetIP can return mapped addresses (see #5698)
for i := range ips {
ips[i] = ips[i].Unmap()
}
have4 := false
for _, ipa := range ips {
if ipa.Is4() {