Add REALLOC macro to simplify realloc error handling

realloc can fail just like the other memory allocation functions. Add a
macro to simplify handling of realloc failures, similar to the already
existing MALLOC, CALLOC, etc.

Replace the existing realloc uses with the new macro, allowing us to
move tedious error handling to the macro. Also, in be_package and
be_sync, this fixes hypothetical memory leaks (and thereafter null
pointer dereferences) in case realloc fails to shrink the allocated
memory.

Signed-off-by: Rikard Falkeborn <rikard.falkeborn@gmail.com>
Signed-off-by: Allan McRae <allan@archlinux.org>

lib/libalpm/be_local.c

@@ -843,12 +843,7 @@ static int local_db_read(alpm_pkg_t *info, int inforeq)
 				}
 				/* attempt to hand back any memory we don't need */
 				if(files_count > 0) {
-					alpm_file_t *newfiles;
-
-					newfiles = realloc(files, sizeof(alpm_file_t) * files_count);
-					if(newfiles != NULL) {
-						files = newfiles;
-					}
+					REALLOC(files, sizeof(alpm_file_t) * files_count, (void)0);
 				} else {
 					FREE(files);
 				}

lib/libalpm/be_package.c

@@ -669,8 +669,7 @@ alpm_pkg_t *_alpm_pkg_load_internal(alpm_handle_t *handle,
 	if(full) {
 		if(newpkg->files.files) {
 			/* attempt to hand back any memory we don't need */
-			newpkg->files.files = realloc(newpkg->files.files,
-					sizeof(alpm_file_t) * newpkg->files.count);
+			REALLOC(newpkg->files.files, sizeof(alpm_file_t) * newpkg->files.count, (void)0);
 			/* "checking for conflicts" requires a sorted list, ensure that here */
 			_alpm_log(handle, ALPM_LOG_DEBUG,
 					"sorting package filelist for %s\n", pkgfile);

lib/libalpm/be_sync.c

@@ -689,7 +689,7 @@ static int sync_db_read(alpm_db_t *db, struct archive *archive,
 				}
 				/* attempt to hand back any memory we don't need */
 				if(files_count > 0) {
-					files = realloc(files, sizeof(alpm_file_t) * files_count);
+					REALLOC(files, sizeof(alpm_file_t) * files_count, (void)0);
 				} else {
 					FREE(files);
 				}

lib/libalpm/util.c

@@ -1427,22 +1427,15 @@ int _alpm_fnmatch(const void *pattern, const void *string)
  */
 void *_alpm_realloc(void **data, size_t *current, const size_t required)
 {
-	char *newdata;
-
-	newdata = realloc(*data, required);
-	if(!newdata) {
-		_alpm_alloc_fail(required);
-		return NULL;
-	}
+	REALLOC(*data, required, return NULL);
 
 	if (*current < required) {
 		/* ensure all new memory is zeroed out, in both the initial
 		 * allocation and later reallocs */
-		memset(newdata + *current, 0, required - *current);
+		memset((char*)*data + *current, 0, required - *current);
 	}
 	*current = required;
-	*data = newdata;
-	return newdata;
+	return *data;
 }
 
 /** This automatically grows data based on current/required.

lib/libalpm/util.h

@@ -53,6 +53,7 @@ void _alpm_alloc_fail(size_t size);
 
 #define MALLOC(p, s, action) do { p = malloc(s); if(p == NULL) { _alpm_alloc_fail(s); action; } } while(0)
 #define CALLOC(p, l, s, action) do { p = calloc(l, s); if(p == NULL) { _alpm_alloc_fail(l * s); action; } } while(0)
+#define REALLOC(p, s, action) do { void* np = realloc(p, s); if(np == NULL) { _alpm_alloc_fail(s); action; } else { p = np; } } while(0)
 /* This strdup macro is NULL safe- copying NULL will yield NULL */
 #define STRDUP(r, s, action) do { if(s != NULL) { r = strdup(s); if(r == NULL) { _alpm_alloc_fail(strlen(s)); action; } } else { r = NULL; } } while(0)
 #define STRNDUP(r, s, l, action) do { if(s != NULL) { r = strndup(s, l); if(r == NULL) { _alpm_alloc_fail(l); action; } } else { r = NULL; } } while(0)