core: Sanitize error text validating refs (e.g. against HTML)

See: https://github.com/projectatomic/rpm-ostree/issues/885

If we get a successful Apache directory listing HTML when fetching what we
intend to be a ref, we'd dump the HTML into the error.

I did some scanning of the pull code, and this was the only case
I saw offhand where we were dumping text out into an error.  Which
makes sense, since most of our formats are binary, the exeptions I
think are just `repo/config` and `repo/refs/`.

Closes: #1015
Approved by: mbarnes

src/libostree/ostree-core.c

@@ -36,6 +36,40 @@
 #define ALIGN_VALUE(this, boundary) \
   (( ((unsigned long)(this)) + (((unsigned long)(boundary)) -1)) & (~(((unsigned long)(boundary))-1)))
 
+/* Return a copy of @input suitable for addition to
+ * a GError message; newlines are quashed, the value
+ * is forced to be UTF-8, is truncated to @maxlen (if maxlen != -1).
+ */
+static char *
+quash_string_for_error_message (const char *input,
+                                ssize_t     len,
+                                ssize_t     maxlen)
+{
+  if (len == -1)
+    len = strlen (input);
+  if (maxlen != -1 && maxlen < len)
+    len = maxlen;
+#if GLIB_CHECK_VERSION(2, 52, 0)
+  G_GNUC_BEGIN_IGNORE_DEPRECATIONS
+  char *buf = g_utf8_make_valid (input, len);
+  G_GNUC_END_IGNORE_DEPRECATIONS
+#else
+  char *buf = g_strndup (input, len);
+#endif
+  for (char *iter = buf; iter && *iter; iter++)
+    {
+      char c = *iter;
+      if (c == '\n')
+        *iter = ' ';
+#if !GLIB_CHECK_VERSION(2, 52, 0)
+      /* No g_utf8_make_valid()?  OK, let's just brute force this. */
+      if (!g_ascii_isprint (c))
+        *iter = ' ';
+#endif
+    }
+  return buf;
+}
+
 static gboolean
 file_header_parse (GVariant         *metadata,
                    GFileInfo       **out_file_info,
@@ -1825,7 +1859,15 @@ ostree_validate_structureof_checksum_string (const char *checksum,
   size_t len = strlen (checksum);
 
   if (len != OSTREE_SHA256_STRING_LEN)
-    return glnx_throw (error, "Invalid rev '%s'", checksum);
+    {
+      /* If we happen to get e.g. an Apache directory listing HTML, don't
+       * dump it all to the error.
+       * https://github.com/projectatomic/rpm-ostree/issues/885
+       */
+      g_autofree char *sanitized = quash_string_for_error_message (checksum, len,
+                                                                   OSTREE_SHA256_STRING_LEN);
+      return glnx_throw (error, "Invalid rev %s", sanitized);
+    }
 
   for (i = 0; i < len; i++)
     {

src/libostree/ostree-repo-pull.c

@@ -876,6 +876,7 @@ scan_dirtree_object (OtPullData   *pull_data,
   return TRUE;
 }
 
+/* Given a @ref, fetch its contents (should be a SHA256 ASCII string) */
 static gboolean
 fetch_ref_contents (OtPullData                 *pull_data,
                     const char                 *main_collection_id,
@@ -901,7 +902,7 @@ fetch_ref_contents (OtPullData                 *pull_data,
   g_strchomp (ret_contents);
 
   if (!ostree_validate_checksum_string (ret_contents, error))
-    return FALSE;
+    return glnx_prefix_error (error, "Fetching %s", filename);
 
   ot_transfer_out_value (out_contents, &ret_contents);
   return TRUE;
@@ -1992,7 +1993,7 @@ load_remote_repo_config (OtPullData    *pull_data,
   g_autoptr(GKeyFile) ret_keyfile = g_key_file_new ();
   if (!g_key_file_load_from_data (ret_keyfile, contents, strlen (contents),
                                   0, error))
-    return FALSE;
+    return glnx_prefix_error (error, "Parsing config");
 
   ot_transfer_out_value (out_keyfile, &ret_keyfile);
   return TRUE;