libreboot-utils: extremely safe(ish) malloc usage

yes, a common thing in C programs is one or all
of the following:

* use after frees
* double free (on non-NULL pointer)
* over-writing currently used pointer (mem leak)

i try to reduce the chance of this in my software,
by running free() through a filter function,
free_if_not_null, that returns if a function
is being freed twice - because it sets NULL
after freeing, but will only free if it's not
null already.

this patch adds two functions: smalloc and vmalloc,
for strings and voids. using these makes the program
abort if:

* non-null pointer given for initialisation
* pointer to pointer is null (of course)
* size of zero given, for malloc (zero bytes)

i myself was caught out by this change, prompting
me to make the following fix in fs_dirname_basename()
inside lib/file.c:

-       char *buf;
+       char *buf = NULL;

Yes.

Signed-off-by: Leah Rowe <leah@libreboot.org>

util/libreboot-utils/lib/file.c

@@ -111,12 +111,11 @@ fsync_dir(const char *path)
 	if (if_err(path == NULL, EFAULT) ||
 	    if_err_sys(slen(path, maxlen, &pathlen) < 0) ||
 	    if_err(pathlen >= maxlen || pathlen < 0, EMSGSIZE) ||
-	    if_err(pathlen == 0, EINVAL)
-	    ||
-	    if_err_sys((dirbuf = malloc(pathlen + 1)) == NULL))
+	    if_err(pathlen == 0, EINVAL))
 		goto err_fsync_dir;
 
-	memcpy(dirbuf, path, pathlen + 1);
+	memcpy(smalloc(&dirbuf, pathlen + 1),
+	    path, pathlen + 1);
 	slash = strrchr(dirbuf, '/');
 
 	if (slash != NULL) {
@@ -862,7 +861,7 @@ fs_dirname_basename(const char *path,
     char **dir, char **base,
     int allow_relative)
 {
-	char *buf;
+	char *buf = NULL;
 	char *slash;
 	size_t len;
 	int rval;
@@ -874,11 +873,10 @@ fs_dirname_basename(const char *path,
 #endif
 
 	if (path == NULL || dir == NULL || base == NULL ||
-	    if_err_sys(slen(path, maxlen, &len) < 0) ||
-	    if_err_sys((buf = malloc(len + 1)) == NULL))
+	    if_err_sys(slen(path, maxlen, &len) < 0))
 		return -1;
 
-	memcpy(buf, path, len + 1);
+	memcpy(smalloc(&buf, len + 1), path, len + 1);
 
 	/* strip trailing slashes */
 	while (len > 1 && buf[len - 1] == '/')