crypt32: Avoid relying on PATH_MAX in import_certs_from_dir helper.

PATH_MAX is not guaranteed to be available on all platforms, and it is 
inadequate as a hardcoded buffer size anyway.

dlls/crypt32/rootstore.c

@@ -326,6 +326,32 @@ static BOOL import_certs_from_file(int fd, HCERTSTORE store)
 static BOOL import_certs_from_path(LPCSTR path, HCERTSTORE store,
  BOOL allow_dir);
 
+static BOOL check_buffer_resize(char **ptr_buf, size_t *buf_size, size_t check_size)
+{
+    if (check_size > *buf_size)
+    {
+        *buf_size = check_size;
+
+        if (*ptr_buf)
+        {
+            char *realloc_buf = CryptMemRealloc(*ptr_buf, *buf_size);
+
+            if (!realloc_buf)
+                return FALSE;
+
+            *ptr_buf = realloc_buf;
+        }
+        else
+        {
+            *ptr_buf = CryptMemAlloc(*buf_size);
+            if (!*ptr_buf)
+                return FALSE;
+        }
+    }
+
+    return TRUE;
+}
+
 /* Opens path, which must be a directory, and imports certificates from every
  * file in the directory into store.
  * Returns TRUE if any certificates were successfully imported.
@@ -341,23 +367,27 @@ static BOOL import_certs_from_dir(LPCSTR path, HCERTSTORE store)
     dir = opendir(path);
     if (dir)
     {
-        size_t bufsize = strlen(path) + 1 + PATH_MAX + 1;
-        char *filebuf = CryptMemAlloc(bufsize);
+        size_t path_len = strlen(path), bufsize = 0;
+        char *filebuf = NULL;
 
-        if (filebuf)
-        {
         struct dirent *entry;
         while ((entry = readdir(dir)))
         {
             if (strcmp(entry->d_name, ".") && strcmp(entry->d_name, ".."))
             {
+                size_t name_len = strlen(entry->d_name);
+
+                if (!check_buffer_resize(&filebuf, &bufsize, path_len + 1 + name_len + 1))
+                {
+                    ERR("Path buffer (re)allocation failed with out of memory condition\n");
+                    break;
+                }
                 snprintf(filebuf, bufsize, "%s/%s", path, entry->d_name);
                 if (import_certs_from_path(filebuf, store, FALSE) && !ret)
                     ret = TRUE;
             }
         }
         CryptMemFree(filebuf);
-        }
         closedir(dir);
     }
     return ret;