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

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Message-ID: <20090127105739.GA5778@ff.dom.local>
Date:	Tue, 27 Jan 2009 10:57:39 +0000
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	David Miller <davem@...emloft.net>, 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

On Tue, Jan 27, 2009 at 10:35:11AM +0000, Jarek Poplawski wrote:
> On Tue, Jan 27, 2009 at 09:09:58PM +1100, Herbert Xu wrote:
> > On Tue, Jan 27, 2009 at 07:54:18AM +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.

tcp_v4_destroy_sock() looks like vulnerable too.

BTW, skb_append_datato_frags() currently doesn't need to use this
sk->sk_sndmsg_page at all - it doesn't use caching between calls.

Jarek P.
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