In the Linux kernel, the following vulnerability has been resolved: fou: Fix null-ptr-deref in GRO. We observed a null-ptr-deref in fou_gro_receive() while shutting down a host. [0] The NULL pointer is sk->sk_user_data, and the offset 8 is of protocol in struct fou. When fou_release() is called due to netns dismantle or explicit tunnel teardown, udp_tunnel_sock_release() sets NULL to sk->sk_user_data. Then, the tunnel socket is destroyed after a single RCU grace period. So, in-flight udp4_gro_receive() could find the socket and execute the FOU GRO handler, where sk->sk_user_data could be NULL. Let's use rcu_dereference_sk_user_data() in fou_from_sock() and add NULL checks in FOU GRO handlers. [0]: BUG: kernel NULL pointer dereference, address: 0000000000000008 PF: supervisor read access in kernel mode PF: error_code(0x0000) - not-present page PGD 80000001032f4067 P4D 80000001032f4067 PUD 103240067 PMD 0 SMP PTI CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.10.216-204.855.amzn2…