linux-kernel - Re: [PATCH 4.4.y] tcp: Fix missing range_truesize enlargement in the backport

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Date:   Wed, 15 Aug 2018 22:02:30 +0200
From:   Michal Kubecek <mkubecek@...e.cz>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Takashi Iwai <tiwai@...e.de>, stable@...r.kernel.org,
        Eric Dumazet <edumazet@...gle.com>,
        "David S . Miller" <davem@...emloft.net>,
        linux-kernel@...r.kernel.org, Jiri Bohac <jbohac@...e.cz>
Subject: Re: [PATCH 4.4.y] tcp: Fix missing range_truesize enlargement in the
 backport

On Wed, Aug 15, 2018 at 01:11:21PM +0200, Greg Kroah-Hartman wrote:
> On Wed, Aug 15, 2018 at 11:58:46AM +0200, Takashi Iwai wrote:
> > The 4.4.y stable backport dc6ae4dffd65 for the upstream commit
> > 3d4bf93ac120 ("tcp: detect malicious patterns in
> > tcp_collapse_ofo_queue()") missed a line that enlarges the
> > range_truesize value, which broke the whole check.
> > 
> > Fixes: dc6ae4dffd65 ("tcp: detect malicious patterns in tcp_collapse_ofo_queue()")
> > Signed-off-by: Takashi Iwai <tiwai@...e.de>
> > ---
> > 
> > Greg, this is a fix-up specific to 4.4.y stable backport that had a
> > slightly different form from upstream fix.  I haven't looked at the
> > older trees, but 4.9.y and later took the upstream fix as is, so this
> > patch isn't needed for them.
> > 
> > The patch hasn't been tested with the real test case, though; let me
> > know if the current code is intended.  Thanks!
> 
> Hm, I did the initial backport, and then Eric showed what I got wrong
> and fixed that up, so being still wrong is not inconceivable at all :)

Takashi's follow-up patch is what makes the backport work the same way
as the original mainline commit 3d4bf93ac120. Without it, range_truesize
will be always equal to truesize of first packet in a contiguous range
so that the condition

  range_truesize != head->truesize

will be always false (and there would be no point having range_truesize
variable at all).

Michal Kubecek