Re: [PATCH bpf-next v6 10/10] selftests/bpf: verify lsm_cgroup struct sock access
From: Andrii Nakryiko <hidden>
Date: 2022-05-09 21:55:46
Also in:
bpf
On Fri, Apr 29, 2022 at 2:16 PM Stanislav Fomichev [off-list ref] wrote:
sk_priority & sk_mark are writable, the rest is readonly. Add new ldx_offset fixups to lookup the offset of struct field. Allow using test.kfunc regardless of prog_type. One interesting thing here is that the verifier doesn't really force me to add NULL checks anywhere :-/ Signed-off-by: Stanislav Fomichev <redacted> --- tools/testing/selftests/bpf/test_verifier.c | 54 ++++++++++++++++++- .../selftests/bpf/verifier/lsm_cgroup.c | 34 ++++++++++++ 2 files changed, 87 insertions(+), 1 deletion(-) create mode 100644 tools/testing/selftests/bpf/verifier/lsm_cgroup.c
[...]
quoted hunk ↗ jump to hunk
diff --git a/tools/testing/selftests/bpf/verifier/lsm_cgroup.c b/tools/testing/selftests/bpf/verifier/lsm_cgroup.c new file mode 100644 index 000000000000..af0efe783511 --- /dev/null +++ b/tools/testing/selftests/bpf/verifier/lsm_cgroup.c@@ -0,0 +1,34 @@ +#define SK_WRITABLE_FIELD(tp, field, size, res) \ +{ \ + .descr = field, \ + .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, 0), \ + /* r2 = *(u64 *)(r1 + offsetof(struct sock, <field>)) */ \ + BPF_LDX_MEM(size, BPF_REG_2, BPF_REG_1, 0), \ + /* *(u64 *)(r1 + offsetof(struct sock, <field>)) = r2 */ \ + BPF_STX_MEM(size, BPF_REG_1, BPF_REG_2, 0), \ + BPF_MOV64_IMM(BPF_REG_0, 1), \ + BPF_EXIT_INSN(), \ + }, \ + .result = res, \ + .errstr = res ? "no write support to 'struct sock' at off" : "", \ + .prog_type = BPF_PROG_TYPE_LSM, \ + .expected_attach_type = BPF_LSM_CGROUP, \ + .kfunc = "socket_post_create", \ + .fixup_ldx = { \ + { "socket", "sk", 1 }, \ + { tp, field, 2 }, \ + { tp, field, 3 }, \ + }, \ +} + +SK_WRITABLE_FIELD("sock_common", "skc_family", BPF_H, REJECT), +SK_WRITABLE_FIELD("sock", "sk_sndtimeo", BPF_DW, REJECT), +SK_WRITABLE_FIELD("sock", "sk_priority", BPF_W, ACCEPT), +SK_WRITABLE_FIELD("sock", "sk_mark", BPF_W, ACCEPT), +SK_WRITABLE_FIELD("sock", "sk_pacing_rate", BPF_DW, REJECT), +
have you tried writing it as C program and adding the test to test_progs? Does something not work there?
+#undef SK_WRITABLE_FIELD -- 2.36.0.464.gb9c8b46e94-goog