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

[Andrew Morton]

On Tue, 26 May 2026 13:38:48 +0200 Chris Gellermann <christian.gellermann@xxxxxxxxxxx> 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@xxxxxxxxxxxxxxx>" to each one.  Please retain David's
ack on both.

Thanks.