[LTP] [PATCH] Modify the test logic of mincore.

[Cyril Hrubis <chrubis@suse.cz>]

Hi!
> Currently mincore has a vulnerability and is easy to be attacked.
> CVE has fixed the vulnerability.
> Please see https://www.linuxkernelcves.com/cves/CVE-2019-5489
> 
> Signed-off-by: zhanglianjie <zhanglianjie@uniontech.com>
> ---
>  testcases/kernel/syscalls/mincore/mincore04.c | 15 ++++++++++-----
>  1 file changed, 10 insertions(+), 5 deletions(-)
> 
> diff --git a/testcases/kernel/syscalls/mincore/mincore04.c b/testcases/kernel/syscalls/mincore/mincore04.c
> index ed0ab7dfa..345dedd9a 100644
> --- a/testcases/kernel/syscalls/mincore/mincore04.c
> +++ b/testcases/kernel/syscalls/mincore/mincore04.c
> @@ -95,12 +95,12 @@ static void test_mincore(void)
>  	locked_pages = count_pages_in_cache();
>  	tst_reap_children();
> 
> -	if (locked_pages == NUM_PAGES)
> -		tst_res(TPASS, "mincore reports all %d pages locked by child process "
> -			"are resident", locked_pages);
> -	else
> -		tst_res(TFAIL, "mincore reports %d pages resident but %d pages "
> +	if (locked_pages == 0)
> +		tst_res(TPASS, "mincore reports %d pages resident but %d pages "
>  			"locked by child process", locked_pages, NUM_PAGES);
> +	else
> +		tst_res(TFAIL, "mincore reports all %d pages locked by child process "
> +			"are resident", locked_pages);
>  }

This does not make any sense, the kernel commit explicitly states that
all mapped pages are reported as in core. We do call mlock() in the
child, which will fault all the pages and lock them in memory. So the
test should work both before and after the fix as well.

The kernel commit in question weakened mincore() in a sense that it's
more likely to report pages in core than it previously was. Now all that
is needed is to fault the pages by reading some bytes from them to make
sure they are reported as in core.

If the test fails for you, something is probably broken at your end.

-- 
Cyril Hrubis
chrubis@suse.cz