CVE-2025-38154

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

bpf, sockmap: Avoid using sk_socket after free when sending

The sk->sk_socket is not locked or referenced in backlog thread, and

during the call to skb_send_sock(), there is a race condition with

the release of sk_socket. All types of sockets(tcp/udp/unix/vsock)

will be affected.

Race conditions:

'''

CPU0 CPU1

backlog::skb_send_sock

sendmsg_unlocked

sock_sendmsg

sock_sendmsg_nosec

close(fd):

...

ops->release() -> sock_map_close()

sk_socket->ops = NULL

free(socket)

sock->ops->sendmsg

^

panic here

'''

The ref of psock become 0 after sock_map_close() executed.

'''

void sock_map_close()

{

...

if (likely(psock)) {

...

// !! here we remove psock and the ref of psock become 0

sock_map_remove_links(sk, psock)

psock = sk_psock_get(sk);

if (unlikely(!psock))

goto no_psock; <=== Control jumps here via goto

...

cancel_delayed_work_sync(&psock->work); <=== not executed

sk_psock_put(sk, psock);

...

}

'''

Based on the fact that we already wait for the workqueue to finish in

sock_map_close() if psock is held, we simply increase the psock

reference count to avoid race conditions.

With this patch, if the backlog thread is running, sock_map_close() will

wait for the backlog thread to complete and cancel all pending work.

If no backlog running, any pending work that hasn't started by then will

fail when invoked by sk_psock_get(), as the psock reference count have

been zeroed, and sk_psock_drop() will cancel all jobs via

cancel_delayed_work_sync().

In summary, we require synchronization to coordinate the backlog thread

and close() thread.

The panic I catched:

'''

Workqueue: events sk_psock_backlog

RIP: 0010:sock_sendmsg+0x21d/0x440

RAX: 0000000000000000 RBX: ffffc9000521fad8 RCX: 0000000000000001

...

Call Trace:

<TASK>

? die_addr+0x40/0xa0

? exc_general_protection+0x14c/0x230

? asm_exc_general_protection+0x26/0x30

? sock_sendmsg+0x21d/0x440

? sock_sendmsg+0x3e0/0x440

? __pfx_sock_sendmsg+0x10/0x10

__skb_send_sock+0x543/0xb70

sk_psock_backlog+0x247/0xb80

...

'''