Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <64ca4c9b.5d0a0220.2f302.b8de@mx.google.com>
Date:   Wed, 2 Aug 2023 14:16:54 +0200
From:   Andrew Kanner <andrew.kanner@gmail.com>
To:     David Ahern <dsahern@gmail.com>
Cc:     davem@davemloft.net, edumazet@google.com, kuba@kernel.org,
        pabeni@redhat.com, jasowang@redhat.com, netdev@vger.kernel.org,
        brouer@redhat.com, jbrouer@redhat.com, john.fastabend@gmail.com,
        linux-kernel@vger.kernel.org,
        linux-kernel-mentees@lists.linuxfoundation.org,
        syzbot+f817490f5bd20541b90a@syzkaller.appspotmail.com
Subject: Re: [PATCH v4 1/2] drivers: net: prevent tun_build_skb() to exceed
 the packet size limit
References: <20230801220710.464-1-andrew.kanner@gmail.com>
 <3fa4d25d-7fea-d25b-fa83-4ada2c550725@gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <3fa4d25d-7fea-d25b-fa83-4ada2c550725@gmail.com>
Precedence: bulk

On Tue, Aug 01, 2023 at 07:07:39PM -0600, David Ahern wrote:
> On 8/1/23 4:07 PM, Andrew Kanner wrote:
> > @@ -1594,7 +1597,13 @@ static bool tun_can_build_skb(struct tun_struct *tun, struct tun_file *tfile,
> >  	if (zerocopy)
> >  		return false;
> >  
> > -	if (SKB_DATA_ALIGN(len + TUN_RX_PAD) +
> > +	rcu_read_lock();
> > +	xdp_prog = rcu_dereference(tun->xdp_prog);
> > +	if (xdp_prog)
> > +		pad += XDP_PACKET_HEADROOM;
> > +	rcu_read_unlock();
> 
> 
> since you do not care about the actual xdp_prog (only that one is set) I
> believe you can use rcu_access_pointer here.

Good point. Thanks, David.

I'll resend both as v5.

The correct cc-list for PATCH 2/2 is also needed. It fixes
net/core/filter.c instead of drivers/net/tun.c now.

pw-bot: changes-requested

-- 
Andrew Kanner