xfrm_user: fix info leak in copy_user_offload()

The memory reserved to dump the xfrm offload state includes padding
bytes of struct xfrm_user_offload added by the compiler for alignment.
Add an explicit memset(0) before filling the buffer to avoid the heap
info leak.

Cc: Steffen Klassert <steffen.klassert@secunet.com>
Fixes: d77e38e612a0 ("xfrm: Add an IPsec hardware offloading API")
Signed-off-by: Mathias Krause <minipli@googlemail.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

net/xfrm/xfrm_user.c

@@ -796,7 +796,7 @@ static int copy_user_offload(struct xfrm_state_offload *xso, struct sk_buff *skb
 		return -EMSGSIZE;
 
 	xuo = nla_data(attr);
-
+	memset(xuo, 0, sizeof(*xuo));
 	xuo->ifindex = xso->dev->ifindex;
 	xuo->flags = xso->flags;