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

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Message-ID: <20090127114805.GA30982@gondor.apana.org.au>
Date:	Tue, 27 Jan 2009 22:48:05 +1100
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Jarek Poplawski <jarkao2@...il.com>
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:
>
> > > 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.

Cheers,
-- 
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Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
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