sk_priority & sk_mark are writable, the rest is readonly.
One interesting thing here is that the verifier doesn't
really force me to add NULL checks anywhere :-/
Signed-off-by: Stanislav Fomichev <sdf@xxxxxxxxxx>
---
.../selftests/bpf/prog_tests/lsm_cgroup.c | 69 +++++++++++++++++++
1 file changed, 69 insertions(+)
diff --git a/tools/testing/selftests/bpf/prog_tests/lsm_cgroup.c b/tools/testing/selftests/bpf/prog_tests/lsm_cgroup.c
index a96057ec7dd4..a730acd9dfdd 100644
--- a/tools/testing/selftests/bpf/prog_tests/lsm_cgroup.c
+++ b/tools/testing/selftests/bpf/prog_tests/lsm_cgroup.c
@@ -270,8 +270,77 @@ static void test_lsm_cgroup_functional(void)
lsm_cgroup__destroy(skel);
}
+static int field_offset(const char *type, const char *field)
+{
+ const struct btf_member *memb;
+ const struct btf_type *tp;
+ const char *name;
+ struct btf *btf;
+ int btf_id;
+ int i;
+
+ btf = btf__load_vmlinux_btf();
+ if (!btf)
+ return -1;
+
+ btf_id = btf__find_by_name_kind(btf, type, BTF_KIND_STRUCT);
+ if (btf_id < 0)
+ return -1;
+
+ tp = btf__type_by_id(btf, btf_id);
+ memb = btf_members(tp);
+
+ for (i = 0; i < btf_vlen(tp); i++) {
+ name = btf__name_by_offset(btf,
+ memb->name_off);
+ if (strcmp(field, name) == 0)
+ return memb->offset / 8;
+ memb++;
+ }
+
+ return -1;
+}
+
+static bool sk_writable_field(const char *type, const char *field, int size)
+{
+ LIBBPF_OPTS(bpf_prog_load_opts, opts,
+ .expected_attach_type = BPF_LSM_CGROUP);
+ struct bpf_insn insns[] = {
+ /* r1 = *(u64 *)(r1 + 0) */
+ BPF_LDX_MEM(BPF_DW, BPF_REG_1, BPF_REG_1, 0),
+ /* r1 = *(u64 *)(r1 + offsetof(struct socket, sk)) */
+ BPF_LDX_MEM(BPF_DW, BPF_REG_1, BPF_REG_1, field_offset("socket", "sk")),
+ /* r2 = *(u64 *)(r1 + offsetof(struct sock, <field>)) */
+ BPF_LDX_MEM(size, BPF_REG_2, BPF_REG_1, field_offset(type, field)),
+ /* *(u64 *)(r1 + offsetof(struct sock, <field>)) = r2 */
+ BPF_STX_MEM(size, BPF_REG_1, BPF_REG_2, field_offset(type, field)),
+ BPF_MOV64_IMM(BPF_REG_0, 1),
+ BPF_EXIT_INSN(),
+ };
+ int fd;
+
+ opts.attach_btf_id = libbpf_find_vmlinux_btf_id("socket_post_create",
+ opts.expected_attach_type);
+
+ fd = bpf_prog_load(BPF_PROG_TYPE_LSM, NULL, "GPL", insns, ARRAY_SIZE(insns), &opts);
+ if (fd >= 0)
+ close(fd);
+ return fd >= 0;
+}
+
+static void test_lsm_cgroup_access(void)
+{
+ ASSERT_FALSE(sk_writable_field("sock_common", "skc_family", BPF_H), "skc_family");
+ ASSERT_FALSE(sk_writable_field("sock", "sk_sndtimeo", BPF_DW), "sk_sndtimeo");
+ ASSERT_TRUE(sk_writable_field("sock", "sk_priority", BPF_W), "sk_priority");
+ ASSERT_TRUE(sk_writable_field("sock", "sk_mark", BPF_W), "sk_mark");
+ ASSERT_FALSE(sk_writable_field("sock", "sk_pacing_rate", BPF_DW), "sk_pacing_rate");
+}
+
void test_lsm_cgroup(void)
{
if (test__start_subtest("functional"))
test_lsm_cgroup_functional();
+ if (test__start_subtest("access"))
+ test_lsm_cgroup_access();
}
--
2.36.1.255.ge46751e96f-goog
