From: Paul Moore <redacted>
Date: Mon, 02 Jul 2018 14:20:52 -0400

-static int ipv6_renew_option(void *ohdr,
-			     struct ipv6_opt_hdr __user *newopt, int newoptlen,
-			     int inherit,
-			     struct ipv6_opt_hdr **hdr,
-			     char **p)
+static void ipv6_renew_option(int renewtype,
+			      struct ipv6_opt_hdr **dest,
+			      struct ipv6_opt_hdr *old,
+			      struct ipv6_opt_hdr *new,
+			      int newtype, char **p)
 {

 ...

+	p += CMSG_ALIGN(ipv6_optlen(*dest));

I don't think this actually advances the pointer in the caller,
you need something like:

	*p += CMSG_ALIGN(ipv6_optlen(*dest));