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

[Michael Kerrisk]

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@xxxxxxxxxxxxxx>:
> > > Hi Daniel,
> > >
> > > On Thu, Oct 23, 2008 at 9:50 AM, Daniel Gollub <dgollub@xxxxxxx>
> > >
> > > 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/
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