[LTP] [PATCH] syscalls/keyctl06: Print TFAIL if keyring_read() returns wrong size

[Eric Biggers]

Hi Xiao,

On Tue, Oct 17, 2017 at 08:53:12PM +0800, Xiao Yang wrote:
> According to keyctl06's message, the mentioned bug is introduced
> by the following patch which is merged into kernel since v3.13:
> 'b2a4df200d57 ("KEYS: Expand the capacity of a keyring")'
> 
> However, we still got the following output before v3.13:
>  tst_test.c:958: INFO: Timeout per run is 0h 05m 00s
>  keyctl06.c:60: BROK: KEYCTL_READ returned 8 but expected 4
> 
> In old kernels, the output exposed that keyring_read() could not
> return the size of data read into buffer, because it just returned
> the size of a keyring.  So i think this issue should be targeted
> as TFAIL.
> 
> Signed-off-by: Xiao Yang <yangx.jy@cn.fujitsu.com>
> ---
>  testcases/kernel/syscalls/keyctl/keyctl06.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/testcases/kernel/syscalls/keyctl/keyctl06.c b/testcases/kernel/syscalls/keyctl/keyctl06.c
> index 8873431..bf30fb6 100644
> --- a/testcases/kernel/syscalls/keyctl/keyctl06.c
> +++ b/testcases/kernel/syscalls/keyctl/keyctl06.c
> @@ -56,7 +56,7 @@ static void do_test(void)
>  		tst_brk(TBROK, "KEYCTL_READ didn't return correct key ID");
>  
>  	if (TEST_RETURN != sizeof(key_serial_t)) {
> -		tst_brk(TBROK, "KEYCTL_READ returned %ld but expected %zu",
> +		tst_brk(TFAIL, "KEYCTL_READ returned %ld but expected %zu",
>  			TEST_RETURN, sizeof(key_serial_t));
>  	}
>  

It was actually pointed out yesterday that the short return value is a bug in
the kernel patch.  The documented behavior of keyctl_read() (as well as the
actual behavior for the other key types that implement it) is to return the full
count on a short read, rather than a short count.  It's not really intuitive but
I'm going to have to fix it with another kernel patch.

For now we probably should just make the test accept both return values:

	if (TEST_RETURN != sizeof(key_serial_t) &&
	    TEST_RETURN != sizeof(key_ids)) {
		tst_brk(TBROK, "KEYCTL_READ returned %ld but expected %zu or %zu",
			TEST_RETURN, sizeof(key_serial_t), sizeof(key_ids));
	}

Then once there is another kernel patch, I'll update the test to reference that
commit too, and accept only TEST_RETURN == sizeof(key_ids).

There is also the question of whether anything should be read at all when the
buffer is too small.  Currently the test assumes that a short read is done.
Unfortunately, there is no simple answer to that question as the documentation
for keyctl_read() and implementations are all inconsistent.

Eric