From 196049a040fa75d8bea80191f7fb5fa4e473d081 Mon Sep 17 00:00:00 2001
From: Daniel <dhaavi@users.noreply.github.com>
Date: Tue, 26 Jan 2021 14:15:07 +0100
Subject: [PATCH 1/2] Check binary path of PID lock

---
 cmds/portmaster-start/lock.go | 38 ++++++++++++++++++++++++++++++-----
 cmds/portmaster-start/run.go  |  5 ++++-
 2 files changed, 37 insertions(+), 6 deletions(-)

diff --git a/cmds/portmaster-start/lock.go b/cmds/portmaster-start/lock.go
index 7d7af1bc..14182069 100644
--- a/cmds/portmaster-start/lock.go
+++ b/cmds/portmaster-start/lock.go
@@ -32,14 +32,42 @@ func checkAndCreateInstanceLock(name string) (pid int32, err error) {
 		return 0, createInstanceLock(lockFilePath)
 	}
 
-	// check if process exists
+	// Check if process exists.
 	p, err := processInfo.NewProcess(int32(parsedPid))
-	if err == nil {
-		return p.Pid, nil
+	if err != nil {
+		// A process with the locked PID does not exist.
+		// This is expected, so we can continue normally.
+		return 0, createInstanceLock(lockFilePath)
 	}
 
-	// else create new lock
-	return 0, createInstanceLock(lockFilePath)
+	// Get the process paths and evaluate and clean them.
+	executingBinaryPath, err := p.Exe()
+	if err != nil {
+		return 0, fmt.Errorf("failed to get path of existing process: %w", err)
+	}
+	cleanedExecutingBinaryPath, err := filepath.EvalSymlinks(executingBinaryPath)
+	if err != nil {
+		return 0, fmt.Errorf("failed to evaluate path of existing process: %w", err)
+	}
+	ownBinaryPath, err := os.Executable()
+	if err != nil {
+		return 0, fmt.Errorf("failed to get path of own process: %w", err)
+	}
+	cleanedOwnBinaryPath, err := filepath.EvalSymlinks(ownBinaryPath)
+	if err != nil {
+		return 0, fmt.Errorf("failed to evaluate path of own process: %w", err)
+	}
+
+	// Check if the binary path matches.
+	if cleanedExecutingBinaryPath != cleanedOwnBinaryPath {
+		// The process with the locked PID belongs to another binary.
+		// As the Portmaster usually starts very early, it will have a low PID,
+		// which could be assigned to another process on next boot.
+		return 0, createInstanceLock(lockFilePath)
+	}
+
+	// Return PID of already running instance.
+	return p.Pid, nil
 }
 
 func createInstanceLock(lockFilePath string) error {
diff --git a/cmds/portmaster-start/run.go b/cmds/portmaster-start/run.go
index 98b0f766..81cd2fe5 100644
--- a/cmds/portmaster-start/run.go
+++ b/cmds/portmaster-start/run.go
@@ -130,7 +130,10 @@ func run(opts *Options, cmdArgs []string) (err error) {
 
 	// check for duplicate instances
 	if opts.ShortIdentifier == "core" || opts.ShortIdentifier == "hub" {
-		pid, _ := checkAndCreateInstanceLock(opts.ShortIdentifier)
+		pid, err := checkAndCreateInstanceLock(opts.ShortIdentifier)
+		if err != nil {
+			return fmt.Errorf("failed to exec lock: %w", err)
+		}
 		if pid != 0 {
 			return fmt.Errorf("another instance of %s is already running: PID %d", opts.Name, pid)
 		}

From 6a1c28249197b8468655dd2bfa8a512b2a41c8f2 Mon Sep 17 00:00:00 2001
From: Daniel <dhaavi@users.noreply.github.com>
Date: Thu, 28 Jan 2021 16:18:42 +0100
Subject: [PATCH 2/2] Implement review suggestion

---
 cmds/portmaster-start/lock.go | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/cmds/portmaster-start/lock.go b/cmds/portmaster-start/lock.go
index 14182069..e2dd56b6 100644
--- a/cmds/portmaster-start/lock.go
+++ b/cmds/portmaster-start/lock.go
@@ -1,6 +1,7 @@
 package main
 
 import (
+	"errors"
 	"fmt"
 	"io/ioutil"
 	"log"
@@ -34,10 +35,16 @@ func checkAndCreateInstanceLock(name string) (pid int32, err error) {
 
 	// Check if process exists.
 	p, err := processInfo.NewProcess(int32(parsedPid))
-	if err != nil {
+	switch {
+	case err == nil:
+		// Process exists, continue.
+	case errors.Is(err, processInfo.ErrorProcessNotRunning):
 		// A process with the locked PID does not exist.
 		// This is expected, so we can continue normally.
 		return 0, createInstanceLock(lockFilePath)
+	default:
+		// There was an internal error getting the process.
+		return 0, err
 	}
 
 	// Get the process paths and evaluate and clean them.