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Message-ID: <CAKH8qBuQ8icMgxiozme=HgXcE5Tm937PwNMjFAn0tSAUcMDaYQ@mail.gmail.com>
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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