linux-kernel - Re: [V4.4-rc6 Regression] af_unix: Revert 'lock

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Date:	Fri, 05 Feb 2016 15:03:18 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Rainer Weikusat <rweikusat@...ileactivedefense.com>
Cc:	davem@...emloft.net, hannes@...essinduktion.org,
	edumazet@...gle.com, dhowells@...hat.com, ying.xue@...driver.com,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"stable@...r.kernel.org" <stable@...r.kernel.org>,
	Joseph Salisbury <joseph.salisbury@...onical.com>
Subject: Re: [V4.4-rc6 Regression] af_unix: Revert 'lock_interruptible' in
 stream receive code

On Fri, 2016-02-05 at 21:44 +0000, Rainer Weikusat wrote:
> The present unix_stream_read_generic contains various code sequences of
> the form
> 
> err = -EDISASTER;
> if (<test>)
> 	goto out;
> 
> This has the unfortunate side effect of possibly causing the error code
> to bleed through to the final
> 
> out:
> 	return copied ? : err;
> 
> and then to be wrongly returned if no data was copied because the caller
> didn't supply a data buffer, as demonstrated by the program available at
> 
> http://pad.lv/1540731
> 
> Change it such that err is only set if an error condition was detected.


Well, if you replace the traditional flow

err = -XXXX;
if (test)
     goto out;

Then please add unlikely() to at least give a hint to the compiler.

if (unlikely(test)) {
    err = -XXX;
    goto out;
}

And please add a 'Fixes: .... ' tag for bug fixes.

Thanks.