efivarfs.c: Call get_efivarfs_path() from a constructor

To avoid having problems when the environment changes (due to setenv()
or whatever), ensure that there's an initial call to
get_efivarfs_path(), and that it duplicates the result into a freshly
allocated string.

Fixes github issue rhboot#154

Signed-off-by: Peter Jones <pjones@redhat.com>

src/efivarfs.c

@@ -6,6 +6,7 @@
 
 #include "fix_coverity.h"
 
+#include <err.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <linux/magic.h>
@@ -28,18 +29,36 @@
 #endif
 
 static char const default_efivarfs_path[] = "/sys/firmware/efi/efivars/";
+static char *efivarfs_path;
 
 static char const *
 get_efivarfs_path(void)
 {
-	static const char *path;
-	if (path)
-		return path;
+	if (efivarfs_path)
+		return efivarfs_path;
+
+	efivarfs_path = secure_getenv("EFIVARFS_PATH");
+	if (efivarfs_path)
+		efivarfs_path = strdup(efivarfs_path);
+	else
+		efivarfs_path = strdup(default_efivarfs_path);
+	return efivarfs_path;
+}
 
-	path = getenv("EFIVARFS_PATH");
-	if (!path)
-		path = default_efivarfs_path;
-	return path;
+static void CONSTRUCTOR
+init_efivarfs_path(void)
+{
+	if (!get_efivarfs_path())
+		err(1, "couldn't allocate memory");
+}
+
+static void DESTRUCTOR
+fini_efivarfs_path(void)
+{
+	if (efivarfs_path) {
+		free(efivarfs_path);
+		efivarfs_path = NULL;
+	}
 }
 
 static int