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

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Message-ID: <31934bf4ccf0f28c74266f9da72b9f2da21a7eff.camel@redhat.com>
Date:   Fri, 08 Jun 2018 18:25:58 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     David Miller <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, tom@...ntonium.net, ktkhai@...tuozzo.com
Subject: Re: [PATCH net] kcm: fix races on sk_receive_queue

On Fri, 2018-06-08 at 10:53 -0400, David Miller wrote:
> 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.

Right. But now I fear the fix should be different: if we drop the skb
on skb_copy_datagram_msg() error, that will cause a behavior change. I
need to think more for a proper fix.

Thank you for the feedback.

Paolo