From ff6c1e191ac9e3955d38e9537501eb92f7e5f357 Mon Sep 17 00:00:00 2001
From: "Ying-Chun Liu (PaulLiu)" <liupa@google.com>
Date: Wed, 26 Aug 2026 00:13:27 +0100
Subject: [PATCH] base: cvd: allocd: Search /usr/sbin for dnsmasq and fix PID
 file path

In Debian, dnsmasq is located in /usr/sbin/dnsmasq which is not typically
in non-root users' $PATH. Add SearchForDnsmasq and DnsmasqPath fallback
helpers similar to IptablesPath. Also fix StopDnsmasq to use CvdDir()
instead of hardcoded /var/run/ and fix inverted file.is_open() logic.

Signed-off-by: Ying-Chun Liu (PaulLiu) <liupa@google.com>
---
 base/cvd/allocd/alloc_utils.cpp | 33 +++++++++++++++++++++++++++++----
 base/cvd/allocd/alloc_utils.h   |  1 +
 2 files changed, 30 insertions(+), 4 deletions(-)

diff --git a/base/cvd/allocd/alloc_utils.cpp b/base/cvd/allocd/alloc_utils.cpp
index c7483747d3b..44c56df590c 100644
--- a/base/cvd/allocd/alloc_utils.cpp
+++ b/base/cvd/allocd/alloc_utils.cpp
@@ -57,6 +57,15 @@ Result<std::string> SearchForIptables() {
   return CF_EXPECT(Search({"/usr/sbin", "/sbin"}, "iptables"));
 }
 
+Result<std::string> SearchForDnsmasq() {
+  Result<std::string> p = Search(cuttlefish::Path(), "dnsmasq");
+  if (p.has_value()) {
+    return p;
+  }
+
+  return CF_EXPECT(Search({"/usr/sbin", "/sbin"}, "dnsmasq"));
+}
+
 }  // namespace
 
 bool CreateEthernetIface(std::string_view name, std::string_view bridge_name) {
@@ -284,11 +293,19 @@ void CleanupBridgeGateway(std::string_view name, std::string_view ipaddr,
 
 bool StartDnsmasq(std::string_view bridge_name, std::string_view gateway,
                   std::string_view dhcp_range) {
+  Result<std::string> dnsmasq_path = DnsmasqPath();
+  if (!dnsmasq_path.has_value()) {
+    LOG(ERROR) << "Could not find dnsmasq binary: "
+               << dnsmasq_path.error().Message();
+    return false;
+  }
+
   auto dns_servers = "8.8.8.8,8.8.4.4";
   auto dns6_servers = "2001:4860:4860::8888,2001:4860:4860::8844";
 
   return Execute(
-             {"dnsmasq", "--port=0", "--strict-order", "--except-interface=lo",
+             {*dnsmasq_path, "--port=0", "--strict-order",
+              "--except-interface=lo",
               absl::StrCat("--interface=", bridge_name),
               absl::StrCat("--listen-address=", gateway), "--bind-interfaces",
               absl::StrCat("--dhcp-range=", dhcp_range),
@@ -305,12 +322,12 @@ bool StartDnsmasq(std::string_view bridge_name, std::string_view gateway,
 bool StopDnsmasq(std::string_view name) {
   std::ifstream file;
   std::string filename =
-      absl::StrFormat("/var/run/cuttlefish-dnsmasq-%s.pid", name);
+      absl::StrCat(CvdDir(), "/cuttlefish-dnsmasq-", name, ".pid");
   LOG(INFO) << "stopping dnsmasq for interface: " << name;
   file.open(filename);
-  if (file.is_open()) {
+  if (!file.is_open()) {
     LOG(INFO) << "dnsmasq file:" << filename
-              << " could not be opened, assume dnsmaq has already stopped";
+              << " could not be opened, assume dnsmasq has already stopped";
     return true;
   }
 
@@ -366,4 +383,12 @@ Result<std::string> IptablesPath() {
   return *iptables_path;
 }
 
+Result<std::string> DnsmasqPath() {
+  static const absl::NoDestructor<std::string> dnsmasq_path(
+      SearchForDnsmasq().value_or(""));
+
+  CF_EXPECT(!dnsmasq_path->empty(), "could not find dnsmasq");
+  return *dnsmasq_path;
+}
+
 }  // namespace cuttlefish
diff --git a/base/cvd/allocd/alloc_utils.h b/base/cvd/allocd/alloc_utils.h
index 471833c9c38..2b7d39de742 100644
--- a/base/cvd/allocd/alloc_utils.h
+++ b/base/cvd/allocd/alloc_utils.h
@@ -53,6 +53,7 @@ struct GatewayConfig {
 
 int RunExternalCommand(const std::string& command);
 Result<std::string> IptablesPath();
+Result<std::string> DnsmasqPath();
 std::optional<std::string> GetUserName(uid_t uid);
 
 bool CreateTap(std::string_view name);