Add rreallocn() to librpmio public API

rreallocn() is like realloc() but with multiplication protection.
Inspired by glibc's reallocarray() but I dislike that name.

While at it, add xmallocn() as a shortcut to rreallocn(NULL, ...) case.

Based on initial patch by Demi Marie Obenour.

rpmio/rpmmalloc.c

@@ -7,6 +7,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <stdio.h>
+#include <stdint.h>
 
 #include "debug.h"
 
@@ -58,6 +59,18 @@ void * rcalloc (size_t nmemb, size_t size)
     return value;
 }
 
+void * rreallocn (void *ptr, size_t nmemb, size_t size)
+{
+    register void *value = NULL;
+    if (size == 0) size++;
+    if (nmemb == 0) nmemb++;
+    if (nmemb < SIZE_MAX / size)
+	value = realloc(ptr, nmemb * size);
+    if (value == NULL)
+	value = vmefail(size);
+    return value;
+}
+
 void * rrealloc (void *ptr, size_t size)
 {
     register void *value;

rpmio/rpmutil.h

@@ -124,6 +124,10 @@ void * rmalloc(size_t size);
 RPM_GNUC_MALLOC RPM_GNUC_ALLOC_SIZE2(1,2)
 void * rcalloc(size_t nmemb, size_t size);
 
+/* Like realloc() but with overflow protection */
+RPM_GNUC_MALLOC RPM_GNUC_ALLOC_SIZE2(2,3)
+void * rreallocn(void * ptr, size_t nmemb, size_t size);
+
 RPM_GNUC_ALLOC_SIZE(2)
 void * rrealloc(void *ptr, size_t size);
 

system.h

@@ -64,8 +64,10 @@ extern int fdatasync(int fildes);
 #include "rpmio/rpmutil.h"
 /* compatibility macros to avoid a mass-renaming all over the codebase */
 #define xmalloc(_size) rmalloc((_size))
+#define xmallocn(_nmemb, _size) rreallocn(NULL, (_nmemb), (_size))
 #define xcalloc(_nmemb, _size) rcalloc((_nmemb), (_size))
 #define xrealloc(_ptr, _size) rrealloc((_ptr), (_size))
+#define xreallocn(_ptr, _size) rreallocn((_ptr), (_nmemb), (_size))
 #define xstrdup(_str) rstrdup((_str))
 #define _free(_ptr) rfree((_ptr))