[AUDIT]: Increase skb->truesize in audit_expand

The recent UDP patch exposed this bug in the audit code.  It
was calling pskb_expand_head without increasing skb->truesize.
The caller of pskb_expand_head needs to do so because that function
is designed to be called in places where truesize is already fixed
and therefore it doesn't update its value.

Because the audit system is using it in a place where the truesize
has not yet been fixed, it needs to update its value manually.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Acked-by: James Morris <jmorris@namei.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

kernel/audit.c

@@ -1200,13 +1200,17 @@ struct audit_buffer *audit_log_start(struct audit_context *ctx, gfp_t gfp_mask,
 static inline int audit_expand(struct audit_buffer *ab, int extra)
 {
 	struct sk_buff *skb = ab->skb;
-	int ret = pskb_expand_head(skb, skb_headroom(skb), extra,
-				   ab->gfp_mask);
+	int oldtail = skb_tailroom(skb);
+	int ret = pskb_expand_head(skb, 0, extra, ab->gfp_mask);
+	int newtail = skb_tailroom(skb);
+
 	if (ret < 0) {
 		audit_log_lost("out of memory in audit_expand");
 		return 0;
 	}
-	return skb_tailroom(skb);
+
+	skb->truesize += newtail - oldtail;
+	return newtail;
 }
 
 /*