linux-kernel - Re: [patch 0/3] [RFC] kernel/glibc mismatch of "readlink" syscall?

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Date:	Tue, 04 Nov 2008 11:20:38 -0500
From:	Michael Kerrisk <mtk.manpages@...glemail.com>
To:	Daniel Gollub <dgollub@...e.de>
CC:	Kai Henningsen <kai.extern@...glemail.com>,
	mtk.manpages@...glemail.com, linux-kernel@...r.kernel.org,
	linux-api@...r.kernel.org, linux-man@...r.kernel.org,
	ltp-list@...ts.sourceforge.net, "A.E. Brouwer" <aeb@....tue.nl>
Subject: Re: [patch 0/3] [RFC] kernel/glibc mismatch of "readlink" syscall?

Daniel,

Daniel Gollub wrote:
> On Friday 31 October 2008 16:02:48 Kai Henningsen wrote:
>> Am Fri, 24 Oct 2008 17:53:25 -0500
>>
>> schrieb "Michael Kerrisk" <mtk.manpages@...glemail.com>:
>>> Hi Daniel,
>>>
>>> On Thu, Oct 23, 2008 at 9:50 AM, Daniel Gollub <dgollub@...e.de>
>>>
>>> wrote:
>>>> EINVAL bufsiz is not positive.
>>> The EINVAL error was added to man-pages-1.18 in 1997 (even though, as
>>> you note, the type was "size_t").  I suspect (this was well before I
>>> had any association with man-pages) that was done to reflect kernel
>>> reality (since one could bypass glibc invoke the syscall directly),
>>> but obviously it is inconsistent with the prototype.
>> Actually, it's not inconsistent as described, though perhaps that is
>> unintentional. "Not positive" isn't the same as "negative", as zero
>> isn't positive either, and zero is certainly a possible value of an
>> unsigned type
> 
> True.

So, at this stage I don't plan to make any change to man-pages.
(Let me know if you think this is the wrong course.)

> But there is still the problem for the ltp syscall test "readlink03", when 
> using the glibc "readlink" interface, by calling readlink with a buffer size 
> of "-1".
> 
> Calling "-1" seems to be a valid code/error-path in the linux syscall 
> "readlink", since there is a check for less-equal zero.
> 
> But the less zero, condition can't be reached via the glibc "readlink" 
> interface since this would cause fortify-check to fail (when buliding with -
> D_FORITFY_SOURCE=2).
> 
> To "workaround" the fortify check, by not compiling the testcase with -
> D_FORTIFY_SOURCE=2, or trying to test the linux readlink interface by calling 
> directly syscall() in the testcase ... both suggestion are just workarounds - 
> no real solutions.
> 
> We could also just remove the testcase of buffer size "-1".
> 
> The problem is still, how to test the "readlink" syscall in LTP?

I'd say: remove this test.  And add one for bufsiz==0 if there isn't one
already.

-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
git://git.kernel.org/pub/scm/docs/man-pages/man-pages.git
man-pages online: http://www.kernel.org/doc/man-pages/online_pages.html
Found a bug? http://www.kernel.org/doc/man-pages/reporting_bugs.html
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