Re: [PATCH] selftest: Fix UB of getline due to missing var init

[Lorenzo Stoakes <ljs@kernel.org>]

On Tue, May 26, 2026 at 11:34:09AM -0700, Andrew Morton wrote:
> On Tue, 26 May 2026 13:38:48 +0200 Chris Gellermann <christian.gellermann@codasip.com> wrote:
>
> > Subject: [PATCH] selftest: Fix UB of getline due to missing var init
>
> hm, what's "UB".  Please expand the acronym.
>
> > Clone3_set_tid uses getline(&line, &len, f) in a loop to read the
> > child's process status. The code expects that getline allocates the
> > buffer for the line on the first loop iteration. For this, glibc[1]
> > requires char *line to be set to NULL:
> >
> > > ssize_t getline(char **restrict lineptr, ...)
> > > If *lineptr is set to NULL before the call, then getline() will
> > > allocate a buffer for storing the line.
> >
> > However, char *line is only declared, leading to an undefined
> > initialization value. Fix this by properly initializing it to NULL.
>
> Does the test crash?  If not, how come?  Luck?
>
> > Same issue fixed in mlock-random-test.
> >
> > [1] https://man7.org/linux/man-pages/man3/getline.3.html
>
> The two affected files are testing significantly different parts of the
> kernel.
>
> > Fixes: 41585bbeeef9 ("selftests: add tests for clone3() with *set_tid")
> > Fixes: 26b4224d9961 ("selftests: expanding more mlock selftest")
>
> And these were separated by three years.
>
> So can you please split this into a two-patch series?  And I suggest
> you add "Cc: <stable@vger.kernel.org>" to each one.  Please retain David's
> ack on both.

Since this looks fine (I also wondered about the fixes too of course), feel free
to add my tag to this too:

Reviewed-by: Lorenzo Stoakes <ljs@kernel.org>

>
> Thanks.

Cheers, Lorenzo