1 files changed, 62 insertions, 0 deletions
diff --git a/resolv/ns_rr_cursor_init.c b/resolv/ns_rr_cursor_init.c
new file mode 100644
index 0000000000..6ee80b30e9
--- /dev/null
+++ b/resolv/ns_rr_cursor_init.c
@@ -0,0 +1,62 @@
+/* Initialize a simple DNS packet parser.
+   Copyright (C) 2022 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <arpa/nameser.h>
+#include <errno.h>
+#include <stdbool.h>
+#include <string.h>
+
+bool
+__ns_rr_cursor_init (struct ns_rr_cursor *c,
+                     const unsigned char *buf, size_t len)
+{
+  c->begin = buf;
+  c->end = buf + len;
+
+  /* Check for header size and 16-bit question count value (it must be 1).  */
+  if (len < 12 || buf[4] != 0 || buf[5] != 1)
+    {
+      __set_errno (EMSGSIZE);
+      c->current = c->end;
+      return false;
+    }
+  c->current = buf + 12;
+
+  int consumed = __ns_name_length_uncompressed (c->current, c->end);
+  if (consumed < 0)
+    {
+      __set_errno (EMSGSIZE);
+      c->current = c->end;
+      c->first_rr = NULL;
+      return false;
+    }
+  c->current += consumed;
+
+  /* Ensure there is room for question type and class.  */
+  if (c->end - c->current < 4)
+    {
+      __set_errno (EMSGSIZE);
+      c->current = c->end;
+      c->first_rr = NULL;
+      return false;
+    }
+  c->current += 4;
+  c->first_rr = c->current;
+
+  return true;
+}