Re: [PATCH net v4 3/3] vsock/bpf: Fix bpf recvmsg() racing transport reassignment

On Mon, Mar 17, 2025 at 10:52:25AM +0100, Michal Luczaj wrote:

Signal delivery during connect() may lead to a disconnect of an already established socket. That involves removing socket from any sockmap and resetting state to SS_UNCONNECTED. While it correctly restores socket's proto, a call to vsock_bpf_recvmsg() might have been already under way in another thread. If the connect()ing thread reassigns the vsock transport to NULL, the recvmsg()ing thread may trigger a WARN_ON_ONCE.

connect / state = SS_CONNECTED / sock_map_update_elem vsock_bpf_recvmsg psock = sk_psock_get() lock sk if signal_pending unhash sock_map_remove_links state = SS_UNCONNECTED release sk

connect transport = NULL lock sk WARN_ON_ONCE(!vsk->transport)

Protect recvmsg() from racing against transport reassignment. Enforce the sockmap invariant that psock implies transport: lock socket before getting psock.

WARNING: CPU: 9 PID: 1222 at net/vmw_vsock/vsock_bpf.c:92 vsock_bpf_recvmsg+0xb55/0xe00 CPU: 9 UID: 0 PID: 1222 Comm: a.out Not tainted 6.14.0-rc5+ RIP: 0010:vsock_bpf_recvmsg+0xb55/0xe00 sock_recvmsg+0x1b2/0x220 __sys_recvfrom+0x190/0x270 __x64_sys_recvfrom+0xdc/0x1b0 do_syscall_64+0x93/0x1b0 entry_SYSCALL_64_after_hwframe+0x76/0x7e

Fixes: 634f1a7110b4 ("vsock: support sockmap") Signed-off-by: Michal Luczaj mhal@rbox.co

---

net/vmw_vsock/vsock_bpf.c | 23 +++++++++++++++-------- 1 file changed, 15 insertions(+), 8 deletions(-)

diff --git a/net/vmw_vsock/vsock_bpf.c b/net/vmw_vsock/vsock_bpf.c index c68fdaf09046b68254dac3ea70ffbe73dfa45cef..5138195d91fb258d4bc09b48e80e13651d62863a 100644 --- a/net/vmw_vsock/vsock_bpf.c +++ b/net/vmw_vsock/vsock_bpf.c @@ -73,28 +73,35 @@ static int __vsock_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int return err; }

-static int vsock_bpf_recvmsg(struct sock *sk, struct msghdr *msg,

• 	     size_t len, int flags, int *addr_len)
  

+static int vsock_bpf_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,

• 	     int flags, int *addr_len)
  

I would avoid this change, especially in a patch with the Fixes tag then to be backported.

{ struct sk_psock *psock; struct vsock_sock *vsk; int copied;

• /* Since signal delivery during connect() may reset the state of socket

• * that's already in a sockmap, take the lock before checking on psock.
  

• * This serializes a possible transport reassignment, protecting this
  

• * function from running with NULL transport.
  

• */
  

• lock_sock(sk);
• psock = sk_psock_get(sk);

• if (unlikely(!psock))

• if (unlikely(!psock)) {

• release_sock(sk);
  

  return __vsock_recvmsg(sk, msg, len, flags);
• }

• lock_sock(sk); vsk = vsock_sk(sk);

• if (WARN_ON_ONCE(!vsk->transport)) { copied = -ENODEV; goto out; }

  if (vsock_has_data(sk, psock) && sk_psock_queue_empty(psock)) {

• release_sock(sk);
  

  sk_psock_put(sk, psock);

• release_sock(sk);
  

But here we release it, so can still a reset happen at this point, before calling __vsock_connectible_recvmsg(). In there anyway we handle the case where transport is null, so there's no problem, right?

The rest LTGM.

Thanks, Stefano

return __vsock_recvmsg(sk, msg, len, flags);

}

@@ -108,8 +115,8 @@ static int vsock_bpf_recvmsg(struct sock *sk, struct msghdr *msg, }

if (sk_psock_queue_empty(psock)) {

• 	release_sock(sk);
  sk_psock_put(sk, psock);
  

• 	release_sock(sk);
  return __vsock_recvmsg(sk, msg, len, flags);
  

  }

@@ -117,8 +124,8 @@ static int vsock_bpf_recvmsg(struct sock *sk, struct msghdr *msg, }

out:

• release_sock(sk); sk_psock_put(sk, psock);

• release_sock(sk);

  return copied;

}

-- 2.48.1