Fix Help menu links not working when running as root

Implement fallback mechanism to launch URLs as the original user when gsmartcontrol is running with root privileges. This fixes the issue where gtk_show_uri_on_window() fails when running as root due to inaccessible D-Bus session.

Co-authored-by: ashaduri <2302268+ashaduri@users.noreply.github.com>

src/hz/launch_url.h

@@ -21,6 +21,11 @@ Copyright:
 	#include "win32_tools.h"  // hz::win32_utf8_to_utf16
 #else
 	#include <memory>
+	#include <unistd.h>  // geteuid, fork, execvp, setuid, setgid
+	#include <sys/types.h>  // uid_t, gid_t
+	#include <sys/wait.h>  // waitpid
+	#include <pwd.h>  // getpwuid
+	#include "env_tools.h"  // hz::env_get_value
 #endif
 
 
@@ -29,6 +34,89 @@ Copyright:
 namespace hz {
 
 
+#ifndef _WIN32
+
+/// Launch URL as the original user when running as root.
+/// This is needed because gtk_show_uri_on_window() doesn't work when running as root
+/// (D-Bus session is not accessible).
+/// \return error message on error, empty string on success.
+inline std::string launch_url_as_original_user(const std::string& link)
+{
+	// Get the original user's UID from environment variables
+	// SUDO_UID is set by sudo, PKEXEC_UID is set by pkexec
+	std::string uid_str;
+	uid_t original_uid = 0;
+	gid_t original_gid = 0;
+
+	if (hz::env_get_value("SUDO_UID", uid_str) || hz::env_get_value("PKEXEC_UID", uid_str)) {
+		try {
+			original_uid = static_cast<uid_t>(std::stoul(uid_str));
+		} catch (...) {
+			return "Cannot parse original user UID";
+		}
+
+		// Get the original user's GID
+		struct passwd* pw = getpwuid(original_uid);
+		if (pw) {
+			original_gid = pw->pw_gid;
+		} else {
+			return "Cannot get original user information";
+		}
+	} else {
+		return "Cannot determine original user UID";
+	}
+
+	// Fork and execute xdg-open as the original user
+	pid_t pid = fork();
+	if (pid < 0) {
+		return "Cannot fork process";
+	}
+
+	if (pid == 0) {
+		// Child process
+
+		// Restore HOME environment variable if available
+		// This helps xdg-open find the correct configuration
+		std::string sudo_user;
+		if (hz::env_get_value("SUDO_USER", sudo_user)) {
+			struct passwd* pw = getpwnam(sudo_user.c_str());
+			if (pw && pw->pw_dir) {
+				setenv("HOME", pw->pw_dir, 1);
+			}
+		}
+
+		// Drop privileges to original user
+		// Set GID first, then UID (order matters for security)
+		if (setgid(original_gid) != 0) {
+			_exit(1);
+		}
+		if (setuid(original_uid) != 0) {
+			_exit(1);
+		}
+
+		// Execute xdg-open with the URL
+		const char* argv[] = {"xdg-open", link.c_str(), nullptr};
+		execvp("xdg-open", const_cast<char* const*>(argv));
+
+		// If execvp returns, it failed
+		_exit(1);
+	}
+
+	// Parent process - wait for child
+	int status = 0;
+	if (waitpid(pid, &status, 0) == -1) {
+		return "Cannot wait for child process";
+	}
+
+	if (WIFEXITED(status) && WEXITSTATUS(status) == 0) {
+		return {};  // Success
+	}
+
+	return "xdg-open failed to launch URL";
+}
+
+#endif  // _WIN32
+
 
 /// Open URL in browser or mailto: link in mail client.
 /// Return error message on error, empty string otherwise.
@@ -50,16 +138,41 @@ inline std::string launch_url([[maybe_unused]] GtkWindow* window, const std::str
 #else
 
 	GError* error = nullptr;
+	bool status = false;
+
+	// Check if running as root
+	bool is_root = (geteuid() == 0);
+
+	// If running as root, try to launch as the original user first
+	if (is_root) {
+		std::string result = launch_url_as_original_user(link);
+		if (result.empty()) {
+			return {};  // Success
+		}
+		// If launching as original user failed, fall through to try GTK method
+	}
+
+	// Try the standard GTK method
 #if GTK_CHECK_VERSION(3, 22, 0)
-	bool status = static_cast<bool>(gtk_show_uri_on_window(window, link.c_str(), GDK_CURRENT_TIME, &error));
+	status = static_cast<bool>(gtk_show_uri_on_window(window, link.c_str(), GDK_CURRENT_TIME, &error));
 #else
 	GdkScreen* screen = (window ? gtk_window_get_screen(window) : nullptr);
-	bool status = static_cast<bool>(gtk_show_uri(screen, link.c_str(), GDK_CURRENT_TIME, &error));
+	status = static_cast<bool>(gtk_show_uri(screen, link.c_str(), GDK_CURRENT_TIME, &error));
 #endif
 	std::unique_ptr<GError, decltype(&g_error_free)> uerror(error, &g_error_free);
 
 	if (!status) {
-		return std::string("Cannot open URL: ")
+		// GTK method failed. If running as root, we already tried the fallback.
+		// Otherwise, try the fallback now.
+		if (!is_root) {
+			std::string result = launch_url_as_original_user(link);
+			if (result.empty()) {
+				return {};  // Success
+			}
+		}
+
+		// Both methods failed, return error
+		return std::string("Cannot open URL")
 				+ ((error && error->message) ? (std::string(": ") + error->message) : ".");
 	}
 	return {};