From: Ido Schimmel Date: Thu, 23 Apr 2026 06:36:07 +0000 (+0300) Subject: vrf: Fix a potential NPD when removing a port from a VRF X-Git-Tag: v7.1-rc2~22^2~35 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=2674d603a9e6970463b2b9ebcf8e31e90beae169;p=thirdparty%2Fkernel%2Flinux.git vrf: Fix a potential NPD when removing a port from a VRF RCU readers that identified a net device as a VRF port using netif_is_l3_slave() assume that a subsequent call to netdev_master_upper_dev_get_rcu() will return a VRF device. They then continue to dereference its l3mdev operations. This assumption is not always correct and can result in a NPD [1]. There is no RCU synchronization when removing a port from a VRF, so it is possible for an RCU reader to see a new master device (e.g., a bridge) that does not have l3mdev operations. Fix by adding RCU synchronization after clearing the IFF_L3MDEV_SLAVE flag. Skip this synchronization when a net device is removed from a VRF as part of its deletion and when the VRF device itself is deleted. In the latter case an RCU grace period will pass by the time RTNL is released. [1] BUG: kernel NULL pointer dereference, address: 0000000000000000 [...] RIP: 0010:l3mdev_fib_table_rcu (net/l3mdev/l3mdev.c:181) [...] Call Trace: l3mdev_fib_table_by_index (net/l3mdev/l3mdev.c:201 net/l3mdev/l3mdev.c:189) __inet_bind (net/ipv4/af_inet.c:499 (discriminator 3)) inet_bind_sk (net/ipv4/af_inet.c:469) __sys_bind (./include/linux/file.h:62 (discriminator 1) ./include/linux/file.h:83 (discriminator 1) net/socket.c:1951 (discriminator 1)) __x64_sys_bind (net/socket.c:1969 (discriminator 1) net/socket.c:1967 (discriminator 1) net/socket.c:1967 (discriminator 1)) do_syscall_64 (arch/x86/entry/syscall_64.c:63 (discriminator 1) arch/x86/entry/syscall_64.c:94 (discriminator 1)) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130) Fixes: fdeea7be88b1 ("net: vrf: Set slave's private flag before linking") Reported-by: Haoze Xie Reported-by: Yifan Wu Reported-by: Juefei Pu Reported-by: Yuan Tan Closes: https://lore.kernel.org/netdev/20260419145332.3988923-1-n05ec@lzu.edu.cn/ Signed-off-by: Ido Schimmel Reviewed-by: David Ahern Link: https://patch.msgid.link/20260423063607.1208202-1-idosch@nvidia.com Signed-off-by: Jakub Kicinski --- diff --git a/drivers/net/vrf.c b/drivers/net/vrf.c index 2cf2dbd1c12f..46209917ae4d 100644 --- a/drivers/net/vrf.c +++ b/drivers/net/vrf.c @@ -1034,6 +1034,7 @@ static int do_vrf_add_slave(struct net_device *dev, struct net_device *port_dev, err: port_dev->priv_flags &= ~IFF_L3MDEV_SLAVE; + synchronize_net(); return ret; } @@ -1053,10 +1054,16 @@ static int vrf_add_slave(struct net_device *dev, struct net_device *port_dev, } /* inverse of do_vrf_add_slave */ -static int do_vrf_del_slave(struct net_device *dev, struct net_device *port_dev) +static int do_vrf_del_slave(struct net_device *dev, struct net_device *port_dev, + bool needs_sync) { netdev_upper_dev_unlink(port_dev, dev); port_dev->priv_flags &= ~IFF_L3MDEV_SLAVE; + /* Make sure that concurrent RCU readers that identified the device + * as a VRF port see a VRF master or no master at all. + */ + if (needs_sync) + synchronize_net(); cycle_netdev(port_dev, NULL); @@ -1065,7 +1072,7 @@ static int do_vrf_del_slave(struct net_device *dev, struct net_device *port_dev) static int vrf_del_slave(struct net_device *dev, struct net_device *port_dev) { - return do_vrf_del_slave(dev, port_dev); + return do_vrf_del_slave(dev, port_dev, true); } static void vrf_dev_uninit(struct net_device *dev) @@ -1619,7 +1626,7 @@ static void vrf_dellink(struct net_device *dev, struct list_head *head) struct list_head *iter; netdev_for_each_lower_dev(dev, port_dev, iter) - vrf_del_slave(dev, port_dev); + do_vrf_del_slave(dev, port_dev, false); vrf_map_unregister_dev(dev); @@ -1751,7 +1758,7 @@ static int vrf_device_event(struct notifier_block *unused, goto out; vrf_dev = netdev_master_upper_dev_get(dev); - vrf_del_slave(vrf_dev, dev); + do_vrf_del_slave(vrf_dev, dev, false); } out: return NOTIFY_DONE;