Re: [PATCH bpf v3 1/4] af_unix: Disable MSG_OOB handling for sockets in sockmap/sockhash

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From: Michal Luczaj <mhal@rbox.co>
Date: Sun,  7 Jul 2024 23:28:22 +0200
> AF_UNIX socket tracks the most recent OOB packet (in its receive queue)
> with an `oob_skb` pointer. BPF redirecting does not account for that: when
> an OOB packet is moved between sockets, `oob_skb` is left outdated. This
> results in a single skb that may be accessed from two different sockets.
> 
> Take the easy way out: silently drop MSG_OOB data targeting any socket that
> is in a sockmap or a sockhash. Note that such silent drop is akin to the
> fate of redirected skb's scm_fp_list (SCM_RIGHTS, SCM_CREDENTIALS).
> 
> For symmetry, forbid MSG_OOB in unix_bpf_recvmsg().
> 
> Suggested-by: Kuniyuki Iwashima <kuniyu@amazon.com>
> Fixes: 314001f0bf92 ("af_unix: Add OOB support")
> Signed-off-by: Michal Luczaj <mhal@rbox.co>

Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>

Thanks!


> ---
>  net/unix/af_unix.c  | 41 ++++++++++++++++++++++++++++++++++++++++-
>  net/unix/unix_bpf.c |  3 +++
>  2 files changed, 43 insertions(+), 1 deletion(-)
> 
> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> index 142f56770b77..11cb5badafb6 100644
> --- a/net/unix/af_unix.c
> +++ b/net/unix/af_unix.c
> @@ -2667,10 +2667,49 @@ static struct sk_buff *manage_oob(struct sk_buff *skb, struct sock *sk,
>  
>  static int unix_stream_read_skb(struct sock *sk, skb_read_actor_t recv_actor)
>  {
> +	struct unix_sock *u = unix_sk(sk);
> +	struct sk_buff *skb;
> +	int err;
> +
>  	if (unlikely(READ_ONCE(sk->sk_state) != TCP_ESTABLISHED))
>  		return -ENOTCONN;
>  
> -	return unix_read_skb(sk, recv_actor);
> +	mutex_lock(&u->iolock);
> +	skb = skb_recv_datagram(sk, MSG_DONTWAIT, &err);
> +	mutex_unlock(&u->iolock);
> +	if (!skb)
> +		return err;
> +
> +#if IS_ENABLED(CONFIG_AF_UNIX_OOB)
> +	if (unlikely(skb == READ_ONCE(u->oob_skb))) {
> +		bool drop = false;
> +
> +		unix_state_lock(sk);
> +
> +		if (sock_flag(sk, SOCK_DEAD)) {
> +			unix_state_unlock(sk);
> +			kfree_skb(skb);
> +			return -ECONNRESET;
> +		}
> +
> +		spin_lock(&sk->sk_receive_queue.lock);
> +		if (likely(skb == u->oob_skb)) {
> +			WRITE_ONCE(u->oob_skb, NULL);
> +			drop = true;
> +		}
> +		spin_unlock(&sk->sk_receive_queue.lock);
> +
> +		unix_state_unlock(sk);
> +
> +		if (drop) {
> +			WARN_ON_ONCE(skb_unref(skb));
> +			kfree_skb(skb);
> +			return -EAGAIN;
> +		}
> +	}
> +#endif
> +
> +	return recv_actor(sk, skb);
>  }
>  
>  static int unix_stream_read_generic(struct unix_stream_read_state *state,
> diff --git a/net/unix/unix_bpf.c b/net/unix/unix_bpf.c
> index bd84785bf8d6..bca2d86ba97d 100644
> --- a/net/unix/unix_bpf.c
> +++ b/net/unix/unix_bpf.c
> @@ -54,6 +54,9 @@ static int unix_bpf_recvmsg(struct sock *sk, struct msghdr *msg,
>  	struct sk_psock *psock;
>  	int copied;
>  
> +	if (flags & MSG_OOB)
> +		return -EOPNOTSUPP;
> +
>  	if (!len)
>  		return 0;
>  
> -- 
> 2.45.2