ip6mr: do not acquire mrt_lock in ioctl(SIOCGETMIFCNT_IN6)

rcu_read_lock() protection is good enough.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/ip6mr.c

@@ -1896,20 +1896,20 @@ int ip6mr_ioctl(struct sock *sk, int cmd, void __user *arg)
 		if (vr.mifi >= mrt->maxvif)
 			return -EINVAL;
 		vr.mifi = array_index_nospec(vr.mifi, mrt->maxvif);
-		read_lock(&mrt_lock);
+		rcu_read_lock();
 		vif = &mrt->vif_table[vr.mifi];
 		if (VIF_EXISTS(mrt, vr.mifi)) {
-			vr.icount = vif->pkt_in;
-			vr.ocount = vif->pkt_out;
-			vr.ibytes = vif->bytes_in;
-			vr.obytes = vif->bytes_out;
-			read_unlock(&mrt_lock);
+			vr.icount = READ_ONCE(vif->pkt_in);
+			vr.ocount = READ_ONCE(vif->pkt_out);
+			vr.ibytes = READ_ONCE(vif->bytes_in);
+			vr.obytes = READ_ONCE(vif->bytes_out);
+			rcu_read_unlock();
 
 			if (copy_to_user(arg, &vr, sizeof(vr)))
 				return -EFAULT;
 			return 0;
 		}
-		read_unlock(&mrt_lock);
+		rcu_read_unlock();
 		return -EADDRNOTAVAIL;
 	case SIOCGETSGCNT_IN6:
 		if (copy_from_user(&sr, arg, sizeof(sr)))
@@ -1971,20 +1971,20 @@ int ip6mr_compat_ioctl(struct sock *sk, unsigned int cmd, void __user *arg)
 		if (vr.mifi >= mrt->maxvif)
 			return -EINVAL;
 		vr.mifi = array_index_nospec(vr.mifi, mrt->maxvif);
-		read_lock(&mrt_lock);
+		rcu_read_lock();
 		vif = &mrt->vif_table[vr.mifi];
 		if (VIF_EXISTS(mrt, vr.mifi)) {
-			vr.icount = vif->pkt_in;
-			vr.ocount = vif->pkt_out;
-			vr.ibytes = vif->bytes_in;
-			vr.obytes = vif->bytes_out;
-			read_unlock(&mrt_lock);
+			vr.icount = READ_ONCE(vif->pkt_in);
+			vr.ocount = READ_ONCE(vif->pkt_out);
+			vr.ibytes = READ_ONCE(vif->bytes_in);
+			vr.obytes = READ_ONCE(vif->bytes_out);
+			rcu_read_unlock();
 
 			if (copy_to_user(arg, &vr, sizeof(vr)))
 				return -EFAULT;
 			return 0;
 		}
-		read_unlock(&mrt_lock);
+		rcu_read_unlock();
 		return -EADDRNOTAVAIL;
 	case SIOCGETSGCNT_IN6:
 		if (copy_from_user(&sr, arg, sizeof(sr)))
@@ -2038,8 +2038,8 @@ static int ip6mr_forward2(struct net *net, struct mr_table *mrt,
 
 #ifdef CONFIG_IPV6_PIMSM_V2
 	if (vif->flags & MIFF_REGISTER) {
-		vif->pkt_out++;
-		vif->bytes_out += skb->len;
+		WRITE_ONCE(vif->pkt_out, vif->pkt_out + 1);
+		WRITE_ONCE(vif->bytes_out, vif->bytes_out + skb->len);
 		vif_dev->stats.tx_bytes += skb->len;
 		vif_dev->stats.tx_packets++;
 		rcu_read_lock();
@@ -2077,8 +2077,8 @@ static int ip6mr_forward2(struct net *net, struct mr_table *mrt,
 	 * result in receiving multiple packets.
 	 */
 	skb->dev = vif_dev;
-	vif->pkt_out++;
-	vif->bytes_out += skb->len;
+	WRITE_ONCE(vif->pkt_out, vif->pkt_out + 1);
+	WRITE_ONCE(vif->bytes_out, vif->bytes_out + skb->len);
 
 	/* We are about to write */
 	/* XXX: extension headers? */
@@ -2168,8 +2168,10 @@ static void ip6_mr_forward(struct net *net, struct mr_table *mrt,
 	}
 
 forward:
-	mrt->vif_table[vif].pkt_in++;
-	mrt->vif_table[vif].bytes_in += skb->len;
+	WRITE_ONCE(mrt->vif_table[vif].pkt_in,
+		   mrt->vif_table[vif].pkt_in + 1);
+	WRITE_ONCE(mrt->vif_table[vif].bytes_in,
+		   mrt->vif_table[vif].bytes_in + skb->len);
 
 	/*
 	 *	Forward the frame