Re: [PATCH bpf-next v2 2/2] selftests/bpf: verify that rebinding to port < 1024 from BPF works

[Martin KaFai Lau]

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.

> 
> Cc: Andrey Ignatov <r...@fb.com>
> Cc: Martin KaFai Lau <ka...@fb.com>
> Signed-off-by: Stanislav Fomichev <s...@google.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.

> +             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
>