Log errors of level CRIT around memory allocations

This is aligned with the "Module Wrtiers' Guide" of pam-linux.

Enable mock_syslog for tests/expand in Autoconf, since tests/expand will now
use syslog(3). Not needed on CMake.

Author: dacav

expand.c

@@ -2,12 +2,14 @@
  * Copyright (C) 2023 Yubico AB - See COPYING
  */
 
+#include <errno.h>
+#include <limits.h>
 #include <stdint.h>
 #include <stdlib.h>
 #include <string.h>
-#include <limits.h>
 
 #include "util.h"
+#include "logging.h"
 
 static int buf_write(uint8_t **dst, size_t *size, const void *src, size_t n) {
   if (*size < n) {
@@ -42,7 +44,11 @@ char *expand_variables(const char *str, const char *user) {
   size_t size = PATH_MAX;
   int ok = -1;
 
-  if (str == NULL || (tail = head = malloc(size)) == NULL) {
+  if (str == NULL)
+    return NULL;
+
+  if ((tail = head = malloc(size)) == NULL) {
+    LOG(LOG_CRIT, "Unable to allocate memory (errno=%d)", errno);
     return NULL;
   }
 

pam-u2f.c

@@ -73,9 +73,13 @@ static char *resolve_authfile_path(const cfg_t *cfg, const struct passwd *user,
     path = cfg->auth_file;
   }
 
-  if (dir == NULL || *dir != '/' || path == NULL ||
-      asprintf(&authfile, "%s/%s", dir, path) == -1)
-    authfile = NULL;
+  if (dir == NULL || *dir != '/' || path == NULL)
+    return NULL;
+
+  if (asprintf(&authfile, "%s/%s", dir, path) == -1) {
+    LOG(LOG_CRIT, "Unable to allocate memory (errno=%d)", errno);
+    return NULL;
+  }
 
   return authfile;
 }

tests/Makefile.am

@@ -16,6 +16,7 @@ get_devices_SOURCES = get_devices.c mock_syslog.c
 get_devices_LDADD = $(top_builddir)/libmodule.la
 
 check_PROGRAMS += expand
+expand_SOURCES = expand.c mock_syslog.c
 expand_LDADD = $(top_builddir)/libmodule.la
 
 check_PROGRAMS += cfg