libcamera: utils: Use internal secure_getenv() implementation

The secure_getenv() call is not provided by all C libraries. Support
this feature by implementing our own version.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/libcamera/include/utils.h

@@ -24,6 +24,8 @@ std::unique_ptr<T> make_unique(Args&&... args)
 	return std::unique_ptr<T>(new T(std::forward<Args>(args)...));
 }
 
+char *secure_getenv(const char *name);
+
 } /* namespace utils */
 
 } /* namespace libcamera */

src/libcamera/log.cpp

@@ -122,7 +122,7 @@ Logger::Logger()
  */
 void Logger::parseLogFile()
 {
-	const char *file = secure_getenv("LIBCAMERA_LOG_FILE");
+	const char *file = utils::secure_getenv("LIBCAMERA_LOG_FILE");
 	if (!file)
 		return;
 
@@ -140,7 +140,7 @@ void Logger::parseLogFile()
  */
 void Logger::parseLogLevels()
 {
-	const char *debug = secure_getenv("LIBCAMERA_LOG_LEVELS");
+	const char *debug = utils::secure_getenv("LIBCAMERA_LOG_LEVELS");
 	if (!debug)
 		return;
 

src/libcamera/utils.cpp

@@ -41,6 +41,28 @@ const char *basename(const char *path)
        return base ? base + 1 : path;
 }
 
+/**
+ * \brief Get an environment variable
+ * \param[in] name The name of the variable to return
+ *
+ * The environment list is searched to find the variable 'name', and the
+ * corresponding string is returned.
+ *
+ * If 'secure execution' is required then this function always returns NULL to
+ * avoid vulnerabilities that could occur if set-user-ID or set-group-ID
+ * programs accidentally trust the environment.
+ *
+ * \returns A pointer to the value in the environment or NULL if the requested
+ * environment variable doesn't exist or if secure execution is required.
+ */
+char *secure_getenv(const char *name)
+{
+	if (getauxval(AT_SECURE))
+		return NULL;
+
+	return getenv(name);
+}
+
 /**
  * \fn libcamera::utils::make_unique(Args &&... args)
  * \brief Constructs an object of type T and wraps it in a std::unique_ptr.