bpf, sockmap: Fix double uncharge the mem of sk_msg

In the Linux kernel, the following vulnerability has been resolved:

bpf, sockmap: Fix double uncharge the mem of sk_msg

If tcp_bpf_sendmsg is running during a tear down operation, psock may be

freed.

tcp_bpf_sendmsg()

tcp_bpf_send_verdict()

sk_msg_return()

tcp_bpf_sendmsg_redir()

unlikely(!psock))

sk_msg_free()

The mem of msg has been uncharged in tcp_bpf_send_verdict() by

sk_msg_return(), and would be uncharged by sk_msg_free() again. When psock

is null, we can simply returning an error code, this would then trigger

the sk_msg_free_nocharge in the error path of __SK_REDIRECT and would have

the side effect of throwing an error up to user space. This would be a

slight change in behavior from user side but would look the same as an

error if the redirect on the socket threw an error.

This issue can cause the following info:

WARNING: CPU: 0 PID: 2136 at net/ipv4/af_inet.c:155 inet_sock_destruct+0x13c/0x260

Call Trace:

<TASK>

__sk_destruct+0x24/0x1f0

sk_psock_destroy+0x19b/0x1c0

process_one_work+0x1b3/0x3c0

worker_thread+0x30/0x350

? process_one_work+0x3c0/0x3c0

kthread+0xe6/0x110

? kthread_complete_and_exit+0x20/0x20

ret_from_fork+0x22/0x30

</TASK>