Matthieu Baerts wrote:
> Hi Willem,
>
> (+ cc MPTCP list)
>
> On 24/11/2023 18:15, Willem de Bruijn wrote:
> > From: Willem de Bruijn <willemb@xxxxxxxxxx>
> >
> > Same init_rng() in both tests. The function reads /dev/urandom to
> > initialize srand(). In case of failure, it falls back onto the
> > entropy in the uninitialized variable. Not sure if this is on purpose.
> > But failure reading urandom should be rare, so just fail hard. While
> > at it, convert to getrandom(). Which man 4 random suggests is simpler
> > and more robust.
> >
> > mptcp_inq.c:525:6:
> > mptcp_connect.c:1131:6:
> >
> > error: variable 'foo' is used uninitialized
> > whenever 'if' condition is false
> > [-Werror,-Wsometimes-uninitialized]
>
> Thank you for the patch!
>
> It looks good to me:
>
> Reviewed-by: Matthieu Baerts <matttbe@xxxxxxxxxx>
>
> > Fixes: 048d19d444be ("mptcp: add basic kselftest for mptcp")
> > Fixes: b51880568f20 ("selftests: mptcp: add inq test case")
> > Cc: Florian Westphal <fw@xxxxxxxxx>
> > Signed-off-by: Willem de Bruijn <willemb@xxxxxxxxxx>
> >
> > ----
> >
> > When input is randomized because this is expected to meaningfully
> > explore edge cases, should we also add
> > 1. logging the random seed to stdout and
> > 2. adding a command line argument to replay from a specific seed
> > I can do this in net-next, if authors find it useful in this case.
>
> I think we should have done that from the beginning, otherwise we cannot
> easily reproduce these edge cases. To be honest, I don't think this
> technique helped to find bugs, and it was probably used here as a good
> habit to increase the coverage. But on the other hand, we might not
> realise some inputs are randomised and can cause instabilities in the
> tests because we don't print anything about that.
>
> So I would say that the minimal thing to do is to log the random seed.
> But it might not be that easy to do, for example 'mptcp_connect' is used
> a lot of time by the .sh scripts: printing this seed number each time
> 'mptcp_connect' is started will "flood" the logs. Maybe we should only
> print that at the end, in case of errors: e.g. in xerror() and
> die_perror() for example, but I see 'exit(1)' is directly used in other
> places...
>
> That's more code to change, but if it is still OK for you to do that,
> please also note that you will need to log this to stderr: mptcp_connect
> prints what has been received from the other peer to stdout.
>
> Because it is more than just adding a 'printf()', I just created a
> ticket in our bug tracker, so anybody can look at that and check all the
> details about that:
>
> https://github.com/multipath-tcp/mptcp_net-next/issues/462
Thanks for the detailed feedback, Matthieu!
Another option to avoid flooding the logs might be to choose a pseudo
random number in the script and pass the explicit value mptcp_connect.
I haven't looked closely, but for transport layer tests it is likely
that the payload is entirely ignored. Bar perhaps checksum coverage.
If it does not increase code coverage, randomization can also just be
turned off.
> > ---
> > tools/testing/selftests/net/mptcp/mptcp_connect.c | 11 ++++-------
> > tools/testing/selftests/net/mptcp/mptcp_inq.c | 11 ++++-------
> > 2 files changed, 8 insertions(+), 14 deletions(-)
> >
> > diff --git a/tools/testing/selftests/net/mptcp/mptcp_connect.c b/tools/testing/selftests/net/mptcp/mptcp_connect.c
> > index c7f9ebeebc2c5..d2043ec3bf6d6 100644
> > --- a/tools/testing/selftests/net/mptcp/mptcp_connect.c
> > +++ b/tools/testing/selftests/net/mptcp/mptcp_connect.c
>
> (...)
>
> > @@ -1125,15 +1126,11 @@ int main_loop_s(int listensock)
> >
> > static void init_rng(void)
> > {
> > - int fd = open("/dev/urandom", O_RDONLY);
> > unsigned int foo;
> >
> > - if (fd > 0) {
>
> I just realised that here, we could have fd == 0 which is a valid value.
> I don't think we would have that when executing the selftests, but
> that's another reason to change this :)
>
> > - int ret = read(fd, &foo, sizeof(foo));
> > -
> > - if (ret < 0)
> > - srand(fd + foo);
> > - close(fd);
> > + if (getrandom(&foo, sizeof(foo), 0) == -1) {
> > + perror("getrandom");
> > + exit(1);
> > }
> >
> > srand(foo);
>
> Cheers,
> Matt
