netdev - Re: [PATCH bpf-next 2/2] selftests/bpf: verify that rebinding to port

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Date:   Thu, 21 Jan 2021 16:24:25 -0800
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Stanislav Fomichev <sdf@...gle.com>
Cc:     Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH bpf-next 2/2] selftests/bpf: verify that rebinding to port
 < 1024 from BPF works

On Thu, Jan 21, 2021 at 4:09 PM <sdf@...gle.com> wrote:
>
> On 01/21, Andrii Nakryiko wrote:
> > On Wed, Jan 20, 2021 at 7:16 PM Stanislav Fomichev <sdf@...gle.com> wrote:
> > >
> > > BPF rewrites from 111 to 111, but it still should mark the port as
> > > "changed".
> > > We also verify that if port isn't touched by BPF, it's still prohibited.
> > >
> > > Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
> > > ---
> > >  .../selftests/bpf/prog_tests/bind_perm.c      | 88 +++++++++++++++++++
> > >  tools/testing/selftests/bpf/progs/bind_perm.c | 36 ++++++++
> > >  2 files changed, 124 insertions(+)
> > >  create mode 100644 tools/testing/selftests/bpf/prog_tests/bind_perm.c
> > >  create mode 100644 tools/testing/selftests/bpf/progs/bind_perm.c
> > >
> > > diff --git a/tools/testing/selftests/bpf/prog_tests/bind_perm.c
> > b/tools/testing/selftests/bpf/prog_tests/bind_perm.c
> > > new file mode 100644
> > > index 000000000000..840a04ac9042
> > > --- /dev/null
> > > +++ b/tools/testing/selftests/bpf/prog_tests/bind_perm.c
> > > @@ -0,0 +1,88 @@
> > > +// SPDX-License-Identifier: GPL-2.0
> > > +#include <test_progs.h>
> > > +#include "bind_perm.skel.h"
> > > +
> > > +#include <sys/types.h>
> > > +#include <sys/socket.h>
> > > +#include <sys/capability.h>
> > > +
> > > +static int duration;
> > > +
> > > +void try_bind(int port, int expected_errno)
> > > +{
> > > +       struct sockaddr_in sin = {};
> > > +       int fd = -1;
> > > +
> > > +       fd = socket(AF_INET, SOCK_STREAM, 0);
> > > +       if (CHECK(fd < 0, "fd", "errno %d", errno))
> > > +               goto close_socket;
> > > +
> > > +       sin.sin_family = AF_INET;
> > > +       sin.sin_port = htons(port);
> > > +
> > > +       errno = 0;
> > > +       bind(fd, (struct sockaddr *)&sin, sizeof(sin));
> > > +       CHECK(errno != expected_errno, "bind", "errno %d, expected %d",
> > > +             errno, expected_errno);
>
> > ASSERT_NEQ() is nicer
> Nice, didn't know these existed. Now we need ASSERT_GT/LE/GE/LE to also
> get rid of those other CHECKs :-)

When I was adding the initial set of ASSERT_XXX() I didn't think we'll
need all those variants, but it turns out they come up pretty
frequently. So while you might be joking, I think it's a good idea to
add them and start using them consistently.

>
> > > +
> > > +close_socket:
> > > +       if (fd >= 0)
> > > +               close(fd);
> > > +}
> > > +
> > > +void cap_net_bind_service(cap_flag_value_t flag)
> > > +{
> > > +       const cap_value_t cap_net_bind_service = CAP_NET_BIND_SERVICE;
> > > +       cap_t caps;
> > > +
> > > +       caps = cap_get_proc();
> > > +       if (CHECK(!caps, "cap_get_proc", "errno %d", errno))
> > > +               goto free_caps;
> > > +
> > > +       if (CHECK(cap_set_flag(caps, CAP_EFFECTIVE, 1,
> > &cap_net_bind_service,
> > > +                              CAP_CLEAR),
> > > +                 "cap_set_flag", "errno %d", errno))
> > > +               goto free_caps;
> > > +
> > > +       if (CHECK(cap_set_flag(caps, CAP_EFFECTIVE, 1,
> > &cap_net_bind_service,
> > > +                              CAP_CLEAR),
> > > +                 "cap_set_flag", "errno %d", errno))
> > > +               goto free_caps;
> > > +
> > > +       if (CHECK(cap_set_proc(caps), "cap_set_proc", "errno %d",
> > errno))
> > > +               goto free_caps;
> > > +
> > > +free_caps:
> > > +       if (CHECK(cap_free(caps), "cap_free", "errno %d", errno))
> > > +               goto free_caps;
> > > +}
> > > +
> > > +void test_bind_perm(void)
> > > +{
> > > +       struct bind_perm *skel;
> > > +       int cgroup_fd;
> > > +
> > > +       cgroup_fd = test__join_cgroup("/bind_perm");
> > > +       if (CHECK(cgroup_fd < 0, "cg-join", "errno %d", errno))
> > > +               return;
> > > +
> > > +       skel = bind_perm__open_and_load();
> > > +       if (CHECK(!skel, "skel-load", "errno %d", errno))
> > > +               goto close_cgroup_fd;
>
> > errno is irrelevant; also use ASSERT_PTR_OK() instead
> Ack, it might be worth unconditionally printing it in your ASSERT_XXX
> macros. Worst case - it's not used, but in general case avoids
> all this "errno %d" boilerplate.

Don't know about that, having unrelated errno everywhere is annoying
and misleading. I'd rather move away from relying on errno so much :)

>
> > > +
> > > +       skel->links.bind_v4_prog =
> > bpf_program__attach_cgroup(skel->progs.bind_v4_prog, cgroup_fd);
> > > +       if (CHECK(IS_ERR(skel->links.bind_v4_prog),
> > > +                 "cg-attach", "bind4 %ld",
> > > +                 PTR_ERR(skel->links.bind_v4_prog)))
>
> > try using ASSERT_PTR_OK instead
> Sure, thanks!