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From: Jakub Sitnicki <jakub@cloudflare.com>
To: Cong Wang <xiyou.wangcong@gmail.com>
Cc: netdev@vger.kernel.org, Cong Wang <cong.wang@bytedance.com>,
	Eric Dumazet <eric.dumazet@gmail.com>,
	John Fastabend <john.fastabend@gmail.com>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Lorenz Bauer <lmb@cloudflare.com>
Subject: Re: [Patch bpf-next] unix_bpf: fix a potential deadlock in unix_dgram_bpf_recvmsg()
Date: Wed, 28 Jul 2021 12:12:13 +0200	[thread overview]
Message-ID: <87h7ge3fya.fsf@cloudflare.com> (raw)
In-Reply-To: <20210723183630.5088-1-xiyou.wangcong@gmail.com>

On Fri, Jul 23, 2021 at 08:36 PM CEST, Cong Wang wrote:
> From: Cong Wang <cong.wang@bytedance.com>
>
> As Eric noticed, __unix_dgram_recvmsg() may acquire u->iolock
> too, so we have to release it before calling this function.
>
> Fixes: 9825d866ce0d ("af_unix: Implement unix_dgram_bpf_recvmsg()")
> Reported-by: Eric Dumazet <eric.dumazet@gmail.com>
> Cc: John Fastabend <john.fastabend@gmail.com>
> Cc: Daniel Borkmann <daniel@iogearbox.net>
> Cc: Jakub Sitnicki <jakub@cloudflare.com>
> Cc: Lorenz Bauer <lmb@cloudflare.com>
> Signed-off-by: Cong Wang <cong.wang@bytedance.com>
> ---
>  net/unix/unix_bpf.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/net/unix/unix_bpf.c b/net/unix/unix_bpf.c
> index db0cda29fb2f..b07cb30e87b1 100644
> --- a/net/unix/unix_bpf.c
> +++ b/net/unix/unix_bpf.c
> @@ -53,8 +53,9 @@ static int unix_dgram_bpf_recvmsg(struct sock *sk, struct msghdr *msg,
>  	mutex_lock(&u->iolock);
>  	if (!skb_queue_empty(&sk->sk_receive_queue) &&
>  	    sk_psock_queue_empty(psock)) {
> -		ret = __unix_dgram_recvmsg(sk, msg, len, flags);
> -		goto out;
> +		mutex_unlock(&u->iolock);
> +		sk_psock_put(sk, psock);
> +		return __unix_dgram_recvmsg(sk, msg, len, flags);
>  	}
>  
>  msg_bytes_ready:
> @@ -68,13 +69,13 @@ static int unix_dgram_bpf_recvmsg(struct sock *sk, struct msghdr *msg,
>  		if (data) {
>  			if (!sk_psock_queue_empty(psock))
>  				goto msg_bytes_ready;
> -			ret = __unix_dgram_recvmsg(sk, msg, len, flags);
> -			goto out;
> +			mutex_unlock(&u->iolock);
> +			sk_psock_put(sk, psock);
> +			return __unix_dgram_recvmsg(sk, msg, len, flags);
>  		}
>  		copied = -EAGAIN;
>  	}
>  	ret = copied;
> -out:
>  	mutex_unlock(&u->iolock);
>  	sk_psock_put(sk, psock);
>  	return ret;

Nit: Can be just `return copied`. `ret` became useless.

Acked-by: Jakub Sitnicki <jakub@cloudflare.com>

  parent reply	other threads:[~2021-07-28 10:12 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-23 18:36 Cong Wang
2021-07-27 16:12 ` John Fastabend
2021-07-28  3:06   ` Cong Wang
2021-07-28 10:12 ` Jakub Sitnicki [this message]
2021-07-28 18:52   ` John Fastabend
2021-07-30 19:45     ` Andrii Nakryiko

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