netdev - Re: [PATCH v3] tcp: splice as many packets as possible at once

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Message-Id: <20090127.090651.237239521.davem@davemloft.net>
Date:	Tue, 27 Jan 2009 09:06:51 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	jarkao2@...il.com
Cc:	herbert@...dor.apana.org.au, zbr@...emap.net, w@....eu,
	dada1@...mosbay.com, ben@...s.com, mingo@...e.hu,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	jens.axboe@...cle.com
Subject: Re: [PATCH v3] tcp: splice as many packets as possible at once

From: Jarek Poplawski <jarkao2@...il.com>
Date: Tue, 27 Jan 2009 12:31:11 +0000

> On Tue, Jan 27, 2009 at 12:16:42PM +0000, Jarek Poplawski wrote:
> > On Tue, Jan 27, 2009 at 10:48:05PM +1100, Herbert Xu wrote:
> > > On Tue, Jan 27, 2009 at 10:35:11AM +0000, Jarek Poplawski wrote:
> > > >
> > > > > > Yes, but ip_append_data() (and skb_append_datato_frags() for
> > > > > > NETIF_F_UFO only, so currently not a problem), uses this differently,
> > > > > > and these pages in sk->sk_sndmsg_page could leak or be used after
> > > > > > kfree. (I didn't track locking in these other places).
> > > > > 
> > > > > It'll be freed when the socket is freed so that should be fine.
> > > > 
> > > > I don't think so: these places can overwrite sk->sk_sndmsg_page left
> > > > after tcp_sendmsg(), or skb_splice_bits() now, with NULL or a new
> > > > pointer without put_page() (they only reference copied chunks and
> > > > expect auto freeing). On the other hand, if tcp_sendmsg() reads after
> > > > them it could use a pointer after the page is freed, I guess.
> > > 
> > > I wasn't referring to the first part of your sentence.  That can't
> > > happen because they're only used for UDP sockets, this is a TCP
> > > socket.
> > 
> > Do you mean this part from ip_append_data() isn't used for TCP?:
> 
> Actually, the beginning part of ip_append_data() should be enough too.
> So I guess I missed your point...

TCP doesn't use ip_append_data(), period.
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