From: Zhang Zhengming <zhangzhengming@xxxxxxxxxx>
There is a crash in the function br_get_link_af_size_filtered,
as the port_exists(dev) is true and the rx_handler_data of dev is NULL.
But the rx_handler_data of dev is correct saved in vmcore.
The oops looks something like:
...
pc : br_get_link_af_size_filtered+0x28/0x1c8 [bridge]
...
Call trace:
br_get_link_af_size_filtered+0x28/0x1c8 [bridge]
if_nlmsg_size+0x180/0x1b0
rtnl_calcit.isra.12+0xf8/0x148
rtnetlink_rcv_msg+0x334/0x370
netlink_rcv_skb+0x64/0x130
rtnetlink_rcv+0x28/0x38
netlink_unicast+0x1f0/0x250
netlink_sendmsg+0x310/0x378
sock_sendmsg+0x4c/0x70
__sys_sendto+0x120/0x150
__arm64_sys_sendto+0x30/0x40
el0_svc_common+0x78/0x130
el0_svc_handler+0x38/0x78
el0_svc+0x8/0xc
In br_add_if(), we found there is no guarantee that
assigning rx_handler_data to dev->rx_handler_data
will before setting the IFF_BRIDGE_PORT bit of priv_flags.
So there is a possible data competition:
CPU 0: CPU 1:
(RCU read lock) (RTNL lock)
rtnl_calcit() br_add_slave()
if_nlmsg_size() br_add_if()
br_get_link_af_size_filtered() -> netdev_rx_handler_register
...
// The order is not guaranteed
... -> dev->priv_flags |= IFF_BRIDGE_PORT;
// The IFF_BRIDGE_PORT bit of priv_flags has been set
-> if (br_port_exists(dev)) {
// The dev->rx_handler_data has NOT been assigned
-> p = br_port_get_rcu(dev);
....
-> rcu_assign_pointer(dev->rx_handler_data, rx_handler_data);
...
Fix this by adding memory barrier instruction to ensure the order.
Signed-off-by: Zhang Zhengming <zhangzhengming@xxxxxxxxxx>
Reviewed-by: Zhao Lei <zhaolei69@xxxxxxxxxx>
Reviewed-by: Wang Xiaogang <wangxiaogang3@xxxxxxxxxx>
---
net/bridge/br_if.c | 6 ++++++
net/bridge/br_netlink.c | 1 +
2 files changed, 7 insertions(+)
diff --git a/net/bridge/br_if.c b/net/bridge/br_if.c
index f7d2f47..42895be 100644
--- a/net/bridge/br_if.c
+++ b/net/bridge/br_if.c
@@ -636,6 +636,12 @@ int br_add_if(struct net_bridge *br, struct net_device *dev,
err = netdev_rx_handler_register(dev, br_get_rx_handler(dev), p);
if (err)
goto err4;
+
+ /* Make sure dev->rx_handler_data is written in netdev_rx_handler_register
+ * before the bit IFF_BRIDGE_PORT of dev->priv_flags is set.
+ * coupled with smp_rmb() in br_get_link_af_size_filtered.
+ */
+ smp_wmb();
dev->priv_flags |= IFF_BRIDGE_PORT;
diff --git a/net/bridge/br_netlink.c b/net/bridge/br_netlink.c
index f2b1343..ccc1fd7 100644
--- a/net/bridge/br_netlink.c
+++ b/net/bridge/br_netlink.c
@@ -103,6 +103,7 @@ static size_t br_get_link_af_size_filtered(const struct net_device *dev,
rcu_read_lock();
if (netif_is_bridge_port(dev)) {
+ smp_rmb(); /* coupled with smp_wmb() in br_add_if() */
p = br_port_get_rcu(dev);
vg = nbp_vlan_group_rcu(p);
} else if (dev->priv_flags & IFF_EBRIDGE) {
--
2.7.4
