Date:   Mon, 25 Jan 2021 15:37:34 -0800
From:   Stanislav Fomichev <sdf@...gle.com>
To:     Martin KaFai Lau <kafai@...com>
Cc:     Netdev <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrey Ignatov <rdna@...com>
Subject: Re: [PATCH bpf-next v2 2/2] selftests/bpf: verify that rebinding to
 port < 1024 from BPF works

On Mon, Jan 25, 2021 at 3:30 PM Martin KaFai Lau <kafai@...com> wrote:
>
> On Mon, Jan 25, 2021 at 09:26:41AM -0800, Stanislav Fomichev 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.
> The description requires an update.
Good point, will update this one and the comment!

> >
> > Cc: Andrey Ignatov <rdna@...com>
> > Cc: Martin KaFai Lau <kafai@...com>
> > Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
> > ---
> >  .../selftests/bpf/prog_tests/bind_perm.c      | 85 +++++++++++++++++++
> >  tools/testing/selftests/bpf/progs/bind_perm.c | 36 ++++++++
> >  2 files changed, 121 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..61307d4494bf
> > --- /dev/null
> > +++ b/tools/testing/selftests/bpf/prog_tests/bind_perm.c
> > @@ -0,0 +1,85 @@
> > +// 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));
> > +     ASSERT_EQ(errno, expected_errno, "bind");
> > +
> > +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))
> These two back-to-back cap_set_flag() looks incorrect.
> Also, the "cap_flag_value_t flag" is unused.
Ah, true, I never reset back CAP_NET_BIND_SERVICE, will fix, thanks!

> > +             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;
> There is a loop.
>
> > +}
> > +
> > +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 (!ASSERT_OK_PTR(skel, "skel"))
> > +             goto close_cgroup_fd;
> > +
> > +     skel->links.bind_v4_prog = bpf_program__attach_cgroup(skel->progs.bind_v4_prog, cgroup_fd);
> > +     if (!ASSERT_OK_PTR(skel, "bind_v4_prog"))
> > +             goto close_skeleton;
> > +
> > +     cap_net_bind_service(CAP_CLEAR);
> > +     try_bind(110, EACCES);
> > +     try_bind(111, 0);
> > +     cap_net_bind_service(CAP_SET);
> > +
> > +close_skeleton:
> > +     bind_perm__destroy(skel);
> > +close_cgroup_fd:
> > +     close(cgroup_fd);
> > +}
> > diff --git a/tools/testing/selftests/bpf/progs/bind_perm.c b/tools/testing/selftests/bpf/progs/bind_perm.c
> > new file mode 100644
> > index 000000000000..31ae8d599796
> > --- /dev/null
> > +++ b/tools/testing/selftests/bpf/progs/bind_perm.c
> > @@ -0,0 +1,36 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +
> > +#include <linux/stddef.h>
> > +#include <linux/bpf.h>
> > +#include <sys/types.h>
> > +#include <sys/socket.h>
> > +#include <bpf/bpf_helpers.h>
> > +#include <bpf/bpf_endian.h>
> > +
> > +SEC("cgroup/bind4")
> > +int bind_v4_prog(struct bpf_sock_addr *ctx)
> > +{
> > +     struct bpf_sock *sk;
> > +     __u32 user_ip4;
> > +     __u16 user_port;
> > +
> > +     sk = ctx->sk;
> > +     if (!sk)
> > +             return 0;
> > +
> > +     if (sk->family != AF_INET)
> > +             return 0;
> > +
> > +     if (ctx->type != SOCK_STREAM)
> > +             return 0;
> > +
> > +     /* Rewriting to the same value should still cause
> > +      * permission check to be bypassed.
> > +      */
> This comment is out dated also.
>
> > +     if (ctx->user_port == bpf_htons(111))
> > +             return 3;
> > +
> > +     return 1;
> > +}
> > +
> > +char _license[] SEC("license") = "GPL";
> > --
> > 2.30.0.280.ga3ce27912f-goog
> >

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