xfrm/compat: prevent potential spectre v1 gadget in xfrm_xlate32_attr()

  int type = nla_type(nla);

  if (type > XFRMA_MAX) {
            return -EOPNOTSUPP;
  }

@type is then used as an array index and can be used
as a Spectre v1 gadget.

  if (nla_len(nla) < compat_policy[type].len) {

array_index_nospec() can be used to prevent leaking
content of kernel memory to malicious users.

Fixes: 5106f4a8 ("xfrm/compat: Add 32=>64-bit messages translator")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Dmitry Safonov <dima@arista.com>
Cc: Steffen Klassert <steffen.klassert@secunet.com>
Reviewed-by: Dmitry Safonov <dima@arista.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

net/xfrm/xfrm_compat.c

@@ -5,6 +5,7 @@
  * Based on code and translator idea by: Florian Westphal <fw@strlen.de>
  */
 #include <linux/compat.h>
+#include <linux/nospec.h>
 #include <linux/xfrm.h>
 #include <net/xfrm.h>
 
@@ -437,6 +438,7 @@ static int xfrm_xlate32_attr(void *dst, const struct nlattr *nla,
 		NL_SET_ERR_MSG(extack, "Bad attribute");
 		return -EOPNOTSUPP;
 	}
+	type = array_index_nospec(type, XFRMA_MAX + 1);
 	if (nla_len(nla) < compat_policy[type].len) {
 		NL_SET_ERR_MSG(extack, "Attribute bad length");
 		return -EOPNOTSUPP;