[PATCH 3.16 111/129] vxlan: test dev->flags & IFF_UP before calling gro_cells_receive()

[Ben Hutchings]

3.16.70-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <edumazet@xxxxxxxxxx>

commit 59cbf56fcd98ba2a715b6e97c4e43f773f956393 upstream.

Same reasons than the ones explained in commit 4179cb5a4c92
("vxlan: test dev->flags & IFF_UP before calling netif_rx()")

netif_rx() or gro_cells_receive() must be called under a strict contract.

At device dismantle phase, core networking clears IFF_UP
and flush_all_backlogs() is called after rcu grace period
to make sure no incoming packet might be in a cpu backlog
and still referencing the device.

A similar protocol is used for gro_cells infrastructure, as
gro_cells_destroy() will be called only after a full rcu
grace period is observed after IFF_UP has been cleared.

Most drivers call netif_rx() from their interrupt handler,
and since the interrupts are disabled at device dismantle,
netif_rx() does not have to check dev->flags & IFF_UP

Virtual drivers do not have this guarantee, and must
therefore make the check themselves.

Otherwise we risk use-after-free and/or crashes.

Fixes: d342894c5d2f ("vxlan: virtual extensible lan")
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
--- a/drivers/net/vxlan.c
+++ b/drivers/net/vxlan.c
@@ -1280,6 +1280,14 @@ static void vxlan_rcv(struct vxlan_sock
 		}
 	}
 
+	rcu_read_lock();
+
+	if (unlikely(!(vxlan->dev->flags & IFF_UP))) {
+		rcu_read_unlock();
+		atomic_long_inc(&vxlan->dev->rx_dropped);
+		goto drop;
+	}
+
 	stats = this_cpu_ptr(vxlan->dev->tstats);
 	u64_stats_update_begin(&stats->syncp);
 	stats->rx_packets++;
@@ -1288,6 +1296,8 @@ static void vxlan_rcv(struct vxlan_sock
 
 	netif_rx(skb);
 
+	rcu_read_unlock();
+
 	return;
 drop:
 	/* Consume bad packet */