From 054ef4de561520290a1147fa21133476beec3ad8 Mon Sep 17 00:00:00 2001
From: Maisem Ali <maisem@tailscale.com>
Date: Mon, 19 Sep 2022 10:36:07 -0700
Subject: [PATCH] tailcfg: mark CapabilityFileSharingTarget as inter-node

Signed-off-by: Maisem Ali <maisem@tailscale.com>
---
 ipn/ipnlocal/local.go | 26 ++++++++++++++++++++------
 tailcfg/tailcfg.go    |  6 +-----
 2 files changed, 21 insertions(+), 11 deletions(-)

diff --git a/ipn/ipnlocal/local.go b/ipn/ipnlocal/local.go
index c721f765f..1cd3cb0be 100644
--- a/ipn/ipnlocal/local.go
+++ b/ipn/ipnlocal/local.go
@@ -24,7 +24,6 @@ import (
 	"time"
 
 	"go4.org/netipx"
-	"golang.org/x/exp/slices"
 	"tailscale.com/client/tailscale/apitype"
 	"tailscale.com/control/controlclient"
 	"tailscale.com/envknob"
@@ -574,6 +573,10 @@ func (b *LocalBackend) WhoIs(ipp netip.AddrPort) (n *tailcfg.Node, u tailcfg.Use
 func (b *LocalBackend) PeerCaps(src netip.Addr) []string {
 	b.mu.Lock()
 	defer b.mu.Unlock()
+	return b.peerCapsLocked(src)
+}
+
+func (b *LocalBackend) peerCapsLocked(src netip.Addr) []string {
 	if b.netMap == nil {
 		return nil
 	}
@@ -585,9 +588,9 @@ func (b *LocalBackend) PeerCaps(src netip.Addr) []string {
 		if !a.IsSingleIP() {
 			continue
 		}
-		dstIP := a.Addr()
-		if dstIP.BitLen() == src.BitLen() {
-			return filt.AppendCaps(nil, src, a.Addr())
+		dst := a.Addr()
+		if dst.BitLen() == src.BitLen() { // match on family
+			return filt.AppendCaps(nil, src, dst)
 		}
 	}
 	return nil
@@ -3304,13 +3307,15 @@ func (b *LocalBackend) FileTargets() ([]*apitype.FileTarget, error) {
 		return nil, errors.New("file sharing not enabled by Tailscale admin")
 	}
 	for _, p := range nm.Peers {
-		if p.User != nm.User && !slices.Contains(p.Capabilities, tailcfg.CapabilityFileSharingTarget) {
+		if len(p.Addresses) == 0 {
+			continue
+		}
+		if p.User != nm.User && b.peerHasCapLocked(p.Addresses[0].Addr(), tailcfg.CapabilityFileSharing) {
 			continue
 		}
 		peerAPI := peerAPIBase(b.netMap, p)
 		if peerAPI == "" {
 			continue
-
 		}
 		ret = append(ret, &apitype.FileTarget{
 			Node:       p,
@@ -3321,6 +3326,15 @@ func (b *LocalBackend) FileTargets() ([]*apitype.FileTarget, error) {
 	return ret, nil
 }
 
+func (b *LocalBackend) peerHasCapLocked(addr netip.Addr, wantCap string) bool {
+	for _, hasCap := range b.peerCapsLocked(addr) {
+		if hasCap == wantCap {
+			return true
+		}
+	}
+	return false
+}
+
 // SetDNS adds a DNS record for the given domain name & TXT record
 // value.
 //
diff --git a/tailcfg/tailcfg.go b/tailcfg/tailcfg.go
index 21c2beac7..7e364e91c 100644
--- a/tailcfg/tailcfg.go
+++ b/tailcfg/tailcfg.go
@@ -1589,15 +1589,11 @@ const (
 	CapabilitySSHRuleIn          = "https://tailscale.com/cap/ssh-rule-in"           // some SSH rule reach this node
 	CapabilityDataPlaneAuditLogs = "https://tailscale.com/cap/data-plane-audit-logs" // feature enabled
 
-	// These are the capabilities that the peer nodes have as listed in
-	// MapResponse.Peers[].Capabilities.
+	// Inter-node capabilities as specified in the MapResponse.PacketFilter[].CapGrants.
 
 	// CapabilityFileSharingTarget grants the current node the ability to send
 	// files to the peer which has this capability.
 	CapabilityFileSharingTarget = "https://tailscale.com/cap/file-sharing-target"
-
-	// Inter-node capabilities as specified in the MapResponse.PacketFilter[].CapGrants.
-
 	// CapabilityFileSharingSend grants the ability to receive files from a
 	// node that's owned by a different user.
 	CapabilityFileSharingSend = "https://tailscale.com/cap/file-send"