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/mkhtemp.c

@@ -144,13 +144,7 @@ new_tmp_common(int *fd, char **path, int type,
 		goto err;
 	}
 
-	dest = malloc(destlen + 1);
-	if (dest == NULL) {
-		errno = ENOMEM;
-		goto err;
-	}
-
-	memcpy(dest, tmpdir, dirlen);
+	memcpy(smalloc(&dest, destlen + 1), tmpdir, dirlen);
 	*(dest + dirlen) = '/';
 	memcpy(dest + dirlen + 1, templatestr, templatestr_len);
 	*(dest + destlen) = '\0';
@@ -585,11 +579,8 @@ mkhtemp(int *fd,
 	      fname_len) != 0, EINVAL))
 		return -1;
 
-	if((fname_copy = malloc(fname_len + 1)) == NULL)
-		goto err;
-
 	/* fname_copy = templatestr region only; p points to trailing XXXXXX */
-	memcpy(fname_copy,
+	memcpy(smalloc(&fname_copy, fname_len + 1),
 	    template + len - fname_len,
 	    fname_len + 1);
 	p = fname_copy + fname_len - xc;