ANDROID: fix a bug in quota2

If quota is precisely equal to skb->len then a notification
would not be sent due to immediately hitting 0.

This fixes that, and takes the opportunity to slightly clean
up the code and make quota behave more correctly for packet mode
as well.

Test: builds, net tests continue to pass
Bug: 164336990
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I78a11b48794496255513a6226c0469d809d7aa56

net/netfilter/xt_quota2.c

@@ -306,6 +306,8 @@ quota_mt2(const struct sk_buff *skb, struct xt_action_param *par)
 {
 	struct xt_quota_mtinfo2 *q = (void *)par->matchinfo;
 	struct xt_quota_counter *e = q->master;
+	int charge = (q->flags & XT_QUOTA_PACKET) ? 1 : skb->len;
+	bool no_change = q->flags & XT_QUOTA_NO_CHANGE;
 	bool ret = q->flags & XT_QUOTA_INVERT;
 
 	spin_lock_bh(&e->lock);
@@ -314,24 +316,21 @@ quota_mt2(const struct sk_buff *skb, struct xt_action_param *par)
 		 * While no_change is pointless in "grow" mode, we will
 		 * implement it here simply to have a consistent behavior.
 		 */
-		if (!(q->flags & XT_QUOTA_NO_CHANGE)) {
-			e->quota += (q->flags & XT_QUOTA_PACKET) ? 1 : skb->len;
-		}
-		ret = true;
+		if (!no_change)
+			e->quota += charge;
+		ret = true; /* note: does not respect inversion (bug??) */
 	} else {
-		if (e->quota >= skb->len) {
-			if (!(q->flags & XT_QUOTA_NO_CHANGE))
-				e->quota -= (q->flags & XT_QUOTA_PACKET) ? 1 : skb->len;
+		if (e->quota > charge) {
+			if (!no_change)
+				e->quota -= charge;
 			ret = !ret;
-		} else {
+		} else if (e->quota) {
 			/* We are transitioning, log that fact. */
-			if (e->quota) {
-				quota2_log(xt_hooknum(par),
-					   skb,
-					   xt_in(par),
-					   xt_out(par),
-					   q->name);
-			}
+			quota2_log(xt_hooknum(par),
+				   skb,
+				   xt_in(par),
+				   xt_out(par),
+				   q->name);
 			/* we do not allow even small packets from now on */
 			e->quota = 0;
 		}