CVE-2026-52925vrf: Fix a potential NPD when removing a port from a VRF

Official description

In the Linux kernel, the following vulnerability has been resolved: 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: <TASK> 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)

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/2c022f582fd16a470df6ed9e7fb7e9fc48946d49
• https://git.kernel.org/stable/c/4ab6fc60ed5a0344b60711b09bff1dc238d8d6a4
• https://git.kernel.org/stable/c/468defa0b70902a22f4478c1207624bc1b31c124
• https://git.kernel.org/stable/c/3db8d078f7f652379ee394132b169d304f6eb4c1
• https://git.kernel.org/stable/c/8c2b792f04a3db97c9d8d2a45817e93f8884baf5
• https://git.kernel.org/stable/c/a7a97f2303e63ede105c1d55ef53dc497364e11d
• https://git.kernel.org/stable/c/d47204c127992da0c976ac9747070a575912e0fe
• https://git.kernel.org/stable/c/2674d603a9e6970463b2b9ebcf8e31e90beae169