[PATCH 5.0 23/43] vxlan: test dev->flags & IFF_UP before calling gro_cells_receive()

From: Greg Kroah-Hartman
Date: Mon Mar 18 2019 - 05:27:07 EST

5.0-stable review patch. If anyone has any objections, please let me know.


From: Eric Dumazet <edumazet@xxxxxxxxxx>

[ Upstream commit 59cbf56fcd98ba2a715b6e97c4e43f773f956393 ]

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
drivers/net/vxlan.c | 11 +++++++++++
1 file changed, 11 insertions(+)

--- a/drivers/net/vxlan.c
+++ b/drivers/net/vxlan.c
@@ -1657,6 +1657,14 @@ static int vxlan_rcv(struct sock *sk, st
goto drop;

+ 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);
@@ -1664,6 +1672,9 @@ static int vxlan_rcv(struct sock *sk, st

gro_cells_receive(&vxlan->gro_cells, skb);
+ rcu_read_unlock();
return 0;