ipn/ipnlocal: normalize IPv6-mapped IPv4 addrs in WhoIs

WhoIs lookups for an IPv6-mapped IPv4 address such as
"::ffff:100.87.98.86" failed to match the node's canonical IPv4
address. Unmap the address before looking it up so these resolve.

Fixes #20235

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Signed-off-by: Bouke van der Bijl <i@bou.ke>

ipn/ipnlocal/local.go

@@ -1730,6 +1730,11 @@ var debugWhoIs = envknob.RegisterBool("TS_DEBUG_WHOIS")
 // If ok == true, n and u are valid.
 func (b *LocalBackend) WhoIs(proto string, ipp netip.AddrPort) (n tailcfg.NodeView, u tailcfg.UserProfile, ok bool) {
 	var zero tailcfg.NodeView
+
+	// Normalize IPv4-mapped IPv6 addresses (e.g. "::ffff:100.87.98.86") to
+	// their canonical IPv4 form so the lookup matches the node's IPv4 address.
+	ipp = netip.AddrPortFrom(ipp.Addr().Unmap(), ipp.Port())
+
 	b.mu.Lock()
 	defer b.mu.Unlock()
 

ipn/ipnlocal/local_test.go

@@ -2904,6 +2904,7 @@ func TestWhoIs(t *testing.T) {
 		{"round1MyselfWithPort", "100.101.102.103:123", 1, "Myself", nil},
 		{"round1Peer2NoPort", "100.200.200.200:0", 2, "Peer2", []string{"group:foo"}},
 		{"round1Peer2WithPort", "100.200.200.200:123", 2, "Peer2", []string{"group:foo"}},
+		{"round1Peer2Mapped4in6", "[::ffff:100.200.200.200]:123", 2, "Peer2", []string{"group:foo"}},
 		{"round1UnknownPeer", "100.4.0.4:404", 0, "", nil},
 	}
 	expectWhois(t, testsRound1, b)