[ 071/102] macvlan: fix passthru mode race between dev removal and rx path

From: Greg Kroah-Hartman
Date: Fri May 17 2013 - 17:42:40 EST

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


From: Jiri Pirko <jiri@xxxxxxxxxxx>

[ Upstream commit 233c7df0821c4190e2d3f4be0f2ca0ab40a5ed8c ]

Currently, if macvlan in passthru mode is created and data are rxed and
you remove this device, following panic happens:

NULL pointer dereference at 0000000000000198
IP: [<ffffffffa0196058>] macvlan_handle_frame+0x153/0x1f7 [macvlan]

I'm using following script to trigger this:
while [ 1 ]
ip link add link e1 name macvtap0 type macvtap mode passthru
ip link set e1 up
ip link set macvtap0 up
IFINDEX=`ip link |grep macvtap0 | cut -f 1 -d ':'`
cat /dev/tap$IFINDEX >/dev/null &
ip link del dev macvtap0

I run this script while "ping -f" is running on another machine to send
packets to e1 rx.

Reason of the panic is that list_first_entry() is blindly called in
macvlan_handle_frame() even if the list was empty. vlan is set to
incorrect pointer which leads to the crash.

I'm fixing this by protecting port->vlans list by rcu and by preventing
from getting incorrect pointer in case the list is empty.

Introduced by: commit eb06acdc85585f2 "macvlan: Introduce 'passthru' mode to takeover the underlying device"

Signed-off-by: Jiri Pirko <jiri@xxxxxxxxxxx>
Acked-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
drivers/net/macvlan.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)

--- a/drivers/net/macvlan.c
+++ b/drivers/net/macvlan.c
@@ -222,7 +222,8 @@ static rx_handler_result_t macvlan_handl

if (port->passthru)
- vlan = list_first_entry(&port->vlans, struct macvlan_dev, list);
+ vlan = list_first_or_null_rcu(&port->vlans,
+ struct macvlan_dev, list);
vlan = macvlan_hash_lookup(port, eth->h_dest);
if (vlan == NULL)
@@ -807,7 +808,7 @@ int macvlan_common_newlink(struct net *s
if (err < 0)
goto upper_dev_unlink;

- list_add_tail(&vlan->list, &port->vlans);
+ list_add_tail_rcu(&vlan->list, &port->vlans);
netif_stacked_transfer_operstate(lowerdev, dev);

return 0;
@@ -835,7 +836,7 @@ void macvlan_dellink(struct net_device *
struct macvlan_dev *vlan = netdev_priv(dev);

- list_del(&vlan->list);
+ list_del_rcu(&vlan->list);
unregister_netdevice_queue(dev, head);
netdev_upper_dev_unlink(vlan->lowerdev, dev);

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