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/include/common.h

@@ -375,6 +375,8 @@ void write_mac_part(size_t partnum);
 
 int xunveilx(const char *path, const char *permissions);
 int xpledgex(const char *promises, const char *execpromises);
+char *smalloc(char **buf, size_t size);
+void *vmalloc(void **buf, size_t size);
 int slen(const char *scmp, size_t maxlen,
     size_t *rval);
 int scmp(const char *a, const char *b,
@@ -393,7 +395,6 @@ int dcat(const char *s, size_t n,
 
 unsigned short hextonum(char ch_s);
 void *mkrbuf(size_t n);
-void *rmalloc(size_t *size); /* don't ever use this */
 void rset(void *buf, size_t n);
 void *mkrbuf(size_t n);
 char *mkrstr(size_t n);