netdev - Re: [PATCH net] kcm: fix races on sk_receive

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Message-Id: <20180608.105311.1644703021787191738.davem@davemloft.net>
Date:   Fri, 08 Jun 2018 10:53:11 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     pabeni@...hat.com
Cc:     netdev@...r.kernel.org, tom@...ntonium.net, ktkhai@...tuozzo.com
Subject: Re: [PATCH net] kcm: fix races on sk_receive_queue

From: Paolo Abeni <pabeni@...hat.com>
Date: Wed,  6 Jun 2018 15:16:29 +0200

> @@ -1126,7 +1132,7 @@ static int kcm_recvmsg(struct socket *sock, struct msghdr *msg,
>  
>  	lock_sock(sk);
>  
> -	skb = kcm_wait_data(sk, flags, timeo, &err);
> +	skb = kcm_wait_data(sk, flags, peek, timeo, &err);
>  	if (!skb)
>  		goto out;
>  

Because kcm_wait_data() potentially unlinks now, you will have to kfree the
SKB in the error paths, for example if skb_copy_datagram_msg() fails.

Otherwise we have an SKB leak.

Yeah, it's kind of ugly that kcm_recvmsg() is going to become a pile of
conditional operations based upon the peek boolean. :-/