This is a note to let you know that I've just added the patch titled bridge: Fix possible races between assigning rx_handler_data and setting IFF_BRIDGE_PORT bit to the 5.12-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: bridge-fix-possible-races-between-assigning-rx_handl.patch and it can be found in the queue-5.12 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 6e27240d41df3c49b71b7667cf3839e66c24bc22 Author: Zhang Zhengming <zhangzhengming@xxxxxxxxxx> Date: Wed Apr 28 22:38:14 2021 +0800 bridge: Fix possible races between assigning rx_handler_data and setting IFF_BRIDGE_PORT bit [ Upstream commit 59259ff7a81b9eb6213891c6451221e567f8f22f ] 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 it in br_get_link_af_size_filtered, using br_port_get_check_rcu() and checking the return value. Signed-off-by: Zhang Zhengming <zhangzhengming@xxxxxxxxxx> Reviewed-by: Zhao Lei <zhaolei69@xxxxxxxxxx> Reviewed-by: Wang Xiaogang <wangxiaogang3@xxxxxxxxxx> Suggested-by: Nikolay Aleksandrov <nikolay@xxxxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/net/bridge/br_netlink.c b/net/bridge/br_netlink.c index 0456593aceec..e4e6e991313e 100644 --- a/net/bridge/br_netlink.c +++ b/net/bridge/br_netlink.c @@ -103,8 +103,9 @@ static size_t br_get_link_af_size_filtered(const struct net_device *dev, rcu_read_lock(); if (netif_is_bridge_port(dev)) { - p = br_port_get_rcu(dev); - vg = nbp_vlan_group_rcu(p); + p = br_port_get_check_rcu(dev); + if (p) + vg = nbp_vlan_group_rcu(p); } else if (dev->priv_flags & IFF_EBRIDGE) { br = netdev_priv(dev); vg = br_vlan_group_rcu(br);