selftests/bpf: Test bpf_strtol and bpf_strtoul helpers

Test that bpf_strtol and  bpf_strtoul helpers can be used to convert
provided buffer to long or unsigned long correspondingly and return both
correct result and number of consumed bytes, or proper errno.

Example of output:
  # ./test_sysctl
  ..
  Test case: bpf_strtoul one number string .. [PASS]
  Test case: bpf_strtoul multi number string .. [PASS]
  Test case: bpf_strtoul buf_len = 0, reject .. [PASS]
  Test case: bpf_strtoul supported base, ok .. [PASS]
  Test case: bpf_strtoul unsupported base, EINVAL .. [PASS]
  Test case: bpf_strtoul buf with spaces only, EINVAL .. [PASS]
  Test case: bpf_strtoul negative number, EINVAL .. [PASS]
  Test case: bpf_strtol negative number, ok .. [PASS]
  Test case: bpf_strtol hex number, ok .. [PASS]
  Test case: bpf_strtol max long .. [PASS]
  Test case: bpf_strtol overflow, ERANGE .. [PASS]
  Summary: 36 PASSED, 0 FAILED

Signed-off-by: Andrey Ignatov <rdna@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/tools/testing/selftests/bpf/test_sysctl.c b/tools/testing/selftests/bpf/test_sysctl.c
index 43008aae32d3d7cae8f039befe5c4c5a4108f17c..885675480af9bbcf85e6685b6f3ab831f697ec4d 100644 (file)
--- a/tools/testing/selftests/bpf/test_sysctl.c
+++ b/tools/testing/selftests/bpf/test_sysctl.c
@@ -817,6 +817,491 @@ static struct sysctl_test tests[] = {
                .newval = "606",
                .result = SUCCESS,
        },
+       {
+               "bpf_strtoul one number string",
+               .insns = {
+                       /* arg1 (buf) */
+                       BPF_MOV64_REG(BPF_REG_7, BPF_REG_10),
+                       BPF_ALU64_IMM(BPF_ADD, BPF_REG_7, -8),
+                       BPF_MOV64_IMM(BPF_REG_0, 0x00303036),
+                       BPF_STX_MEM(BPF_DW, BPF_REG_7, BPF_REG_0, 0),
+
+                       BPF_MOV64_REG(BPF_REG_1, BPF_REG_7),
+
+                       /* arg2 (buf_len) */
+                       BPF_MOV64_IMM(BPF_REG_2, 4),
+
+                       /* arg3 (flags) */
+                       BPF_MOV64_IMM(BPF_REG_3, 0),
+
+                       /* arg4 (res) */
+                       BPF_ALU64_IMM(BPF_ADD, BPF_REG_7, -8),
+                       BPF_STX_MEM(BPF_DW, BPF_REG_7, BPF_REG_0, 0),
+                       BPF_MOV64_REG(BPF_REG_4, BPF_REG_7),
+
+                       BPF_EMIT_CALL(BPF_FUNC_strtoul),
+
+                       /* if (ret == expected && */
+                       BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 3, 4),
+                       /*     res == expected) */
+                       BPF_LDX_MEM(BPF_DW, BPF_REG_9, BPF_REG_7, 0),
+                       BPF_JMP_IMM(BPF_JNE, BPF_REG_9, 600, 2),
+
+                       /* return ALLOW; */
+                       BPF_MOV64_IMM(BPF_REG_0, 1),
+                       BPF_JMP_A(1),
+
+                       /* else return DENY; */
+                       BPF_MOV64_IMM(BPF_REG_0, 0),
+                       BPF_EXIT_INSN(),
+               },
+               .attach_type = BPF_CGROUP_SYSCTL,
+               .sysctl = "net/ipv4/route/mtu_expires",
+               .open_flags = O_RDONLY,
+               .result = SUCCESS,
+       },
+       {
+               "bpf_strtoul multi number string",
+               .insns = {
+                       /* arg1 (buf) */
+                       BPF_MOV64_REG(BPF_REG_7, BPF_REG_10),
+                       BPF_ALU64_IMM(BPF_ADD, BPF_REG_7, -8),
+                       /* "600 602\0" */
+                       BPF_LD_IMM64(BPF_REG_0, 0x0032303620303036ULL),
+                       BPF_STX_MEM(BPF_DW, BPF_REG_7, BPF_REG_0, 0),
+                       BPF_MOV64_REG(BPF_REG_1, BPF_REG_7),
+
+                       /* arg2 (buf_len) */
+                       BPF_MOV64_IMM(BPF_REG_2, 8),
+
+                       /* arg3 (flags) */
+                       BPF_MOV64_IMM(BPF_REG_3, 0),
+
+                       /* arg4 (res) */
+                       BPF_ALU64_IMM(BPF_ADD, BPF_REG_7, -8),
+                       BPF_STX_MEM(BPF_DW, BPF_REG_7, BPF_REG_0, 0),
+                       BPF_MOV64_REG(BPF_REG_4, BPF_REG_7),
+
+                       BPF_EMIT_CALL(BPF_FUNC_strtoul),
+
+                       /* if (ret == expected && */
+                       BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 3, 18),
+                       /*     res == expected) */
+                       BPF_LDX_MEM(BPF_DW, BPF_REG_9, BPF_REG_7, 0),
+                       BPF_JMP_IMM(BPF_JNE, BPF_REG_9, 600, 16),
+
+                       /*     arg1 (buf) */
+                       BPF_MOV64_REG(BPF_REG_7, BPF_REG_10),
+                       BPF_ALU64_IMM(BPF_ADD, BPF_REG_7, -8),
+                       BPF_ALU64_REG(BPF_ADD, BPF_REG_7, BPF_REG_0),
+                       BPF_MOV64_REG(BPF_REG_1, BPF_REG_7),
+
+                       /*     arg2 (buf_len) */
+                       BPF_MOV64_IMM(BPF_REG_2, 8),
+                       BPF_ALU64_REG(BPF_SUB, BPF_REG_2, BPF_REG_0),
+
+                       /*     arg3 (flags) */
+                       BPF_MOV64_IMM(BPF_REG_3, 0),
+
+                       /*     arg4 (res) */
+                       BPF_MOV64_REG(BPF_REG_7, BPF_REG_10),
+                       BPF_ALU64_IMM(BPF_ADD, BPF_REG_7, -16),
+                       BPF_MOV64_REG(BPF_REG_4, BPF_REG_7),
+
+                       BPF_EMIT_CALL(BPF_FUNC_strtoul),
+
+                       /*     if (ret == expected && */
+                       BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 4, 4),
+                       /*         res == expected) */
+                       BPF_LDX_MEM(BPF_DW, BPF_REG_9, BPF_REG_7, 0),
+                       BPF_JMP_IMM(BPF_JNE, BPF_REG_9, 602, 2),
+
+                       /* return ALLOW; */
+                       BPF_MOV64_IMM(BPF_REG_0, 1),
+                       BPF_JMP_A(1),
+
+                       /* else return DENY; */
+                       BPF_MOV64_IMM(BPF_REG_0, 0),
+                       BPF_EXIT_INSN(),
+               },
+               .attach_type = BPF_CGROUP_SYSCTL,
+               .sysctl = "net/ipv4/tcp_mem",
+               .open_flags = O_RDONLY,
+               .result = SUCCESS,
+       },
+       {
+               "bpf_strtoul buf_len = 0, reject",
+               .insns = {
+                       /* arg1 (buf) */
+                       BPF_MOV64_REG(BPF_REG_7, BPF_REG_10),
+                       BPF_ALU64_IMM(BPF_ADD, BPF_REG_7, -8),
+                       BPF_MOV64_IMM(BPF_REG_0, 0x00303036),
+                       BPF_STX_MEM(BPF_DW, BPF_REG_7, BPF_REG_0, 0),
+
+                       BPF_MOV64_REG(BPF_REG_1, BPF_REG_7),
+
+                       /* arg2 (buf_len) */
+                       BPF_MOV64_IMM(BPF_REG_2, 0),
+
+                       /* arg3 (flags) */
+                       BPF_MOV64_IMM(BPF_REG_3, 0),
+
+                       /* arg4 (res) */
+                       BPF_ALU64_IMM(BPF_ADD, BPF_REG_7, -8),
+                       BPF_STX_MEM(BPF_DW, BPF_REG_7, BPF_REG_0, 0),
+                       BPF_MOV64_REG(BPF_REG_4, BPF_REG_7),
+
+                       BPF_EMIT_CALL(BPF_FUNC_strtoul),
+
+                       BPF_MOV64_IMM(BPF_REG_0, 1),
+                       BPF_EXIT_INSN(),
+               },
+               .attach_type = BPF_CGROUP_SYSCTL,
+               .sysctl = "net/ipv4/route/mtu_expires",
+               .open_flags = O_RDONLY,
+               .result = LOAD_REJECT,
+       },
+       {
+               "bpf_strtoul supported base, ok",
+               .insns = {
+                       /* arg1 (buf) */
+                       BPF_MOV64_REG(BPF_REG_7, BPF_REG_10),
+                       BPF_ALU64_IMM(BPF_ADD, BPF_REG_7, -8),
+                       BPF_MOV64_IMM(BPF_REG_0, 0x00373730),
+                       BPF_STX_MEM(BPF_DW, BPF_REG_7, BPF_REG_0, 0),
+
+                       BPF_MOV64_REG(BPF_REG_1, BPF_REG_7),
+
+                       /* arg2 (buf_len) */
+                       BPF_MOV64_IMM(BPF_REG_2, 4),
+
+                       /* arg3 (flags) */
+                       BPF_MOV64_IMM(BPF_REG_3, 8),
+
+                       /* arg4 (res) */
+                       BPF_ALU64_IMM(BPF_ADD, BPF_REG_7, -8),
+                       BPF_STX_MEM(BPF_DW, BPF_REG_7, BPF_REG_0, 0),
+                       BPF_MOV64_REG(BPF_REG_4, BPF_REG_7),
+
+                       BPF_EMIT_CALL(BPF_FUNC_strtoul),
+
+                       /* if (ret == expected && */
+                       BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 3, 4),
+                       /*     res == expected) */
+                       BPF_LDX_MEM(BPF_DW, BPF_REG_9, BPF_REG_7, 0),
+                       BPF_JMP_IMM(BPF_JNE, BPF_REG_9, 63, 2),
+
+                       /* return ALLOW; */
+                       BPF_MOV64_IMM(BPF_REG_0, 1),
+                       BPF_JMP_A(1),
+
+                       /* else return DENY; */
+                       BPF_MOV64_IMM(BPF_REG_0, 0),
+                       BPF_EXIT_INSN(),
+               },
+               .attach_type = BPF_CGROUP_SYSCTL,
+               .sysctl = "net/ipv4/route/mtu_expires",
+               .open_flags = O_RDONLY,
+               .result = SUCCESS,
+       },
+       {
+               "bpf_strtoul unsupported base, EINVAL",
+               .insns = {
+                       /* arg1 (buf) */
+                       BPF_MOV64_REG(BPF_REG_7, BPF_REG_10),
+                       BPF_ALU64_IMM(BPF_ADD, BPF_REG_7, -8),
+                       BPF_MOV64_IMM(BPF_REG_0, 0x00303036),
+                       BPF_STX_MEM(BPF_DW, BPF_REG_7, BPF_REG_0, 0),
+
+                       BPF_MOV64_REG(BPF_REG_1, BPF_REG_7),
+
+                       /* arg2 (buf_len) */
+                       BPF_MOV64_IMM(BPF_REG_2, 4),
+
+                       /* arg3 (flags) */
+                       BPF_MOV64_IMM(BPF_REG_3, 3),
+
+                       /* arg4 (res) */
+                       BPF_ALU64_IMM(BPF_ADD, BPF_REG_7, -8),
+                       BPF_STX_MEM(BPF_DW, BPF_REG_7, BPF_REG_0, 0),
+                       BPF_MOV64_REG(BPF_REG_4, BPF_REG_7),
+
+                       BPF_EMIT_CALL(BPF_FUNC_strtoul),
+
+                       /* if (ret == expected) */
+                       BPF_JMP_IMM(BPF_JNE, BPF_REG_0, -EINVAL, 2),
+
+                       /* return ALLOW; */
+                       BPF_MOV64_IMM(BPF_REG_0, 1),
+                       BPF_JMP_A(1),
+
+                       /* else return DENY; */
+                       BPF_MOV64_IMM(BPF_REG_0, 0),
+                       BPF_EXIT_INSN(),
+               },
+               .attach_type = BPF_CGROUP_SYSCTL,
+               .sysctl = "net/ipv4/route/mtu_expires",
+               .open_flags = O_RDONLY,
+               .result = SUCCESS,
+       },
+       {
+               "bpf_strtoul buf with spaces only, EINVAL",
+               .insns = {
+                       /* arg1 (buf) */
+                       BPF_MOV64_REG(BPF_REG_7, BPF_REG_10),
+                       BPF_ALU64_IMM(BPF_ADD, BPF_REG_7, -8),
+                       BPF_MOV64_IMM(BPF_REG_0, 0x090a0c0d),
+                       BPF_STX_MEM(BPF_DW, BPF_REG_7, BPF_REG_0, 0),
+
+                       BPF_MOV64_REG(BPF_REG_1, BPF_REG_7),
+
+                       /* arg2 (buf_len) */
+                       BPF_MOV64_IMM(BPF_REG_2, 4),
+
+                       /* arg3 (flags) */
+                       BPF_MOV64_IMM(BPF_REG_3, 0),
+
+                       /* arg4 (res) */
+                       BPF_ALU64_IMM(BPF_ADD, BPF_REG_7, -8),
+                       BPF_STX_MEM(BPF_DW, BPF_REG_7, BPF_REG_0, 0),
+                       BPF_MOV64_REG(BPF_REG_4, BPF_REG_7),
+
+                       BPF_EMIT_CALL(BPF_FUNC_strtoul),
+
+                       /* if (ret == expected) */
+                       BPF_JMP_IMM(BPF_JNE, BPF_REG_0, -EINVAL, 2),
+
+                       /* return ALLOW; */
+                       BPF_MOV64_IMM(BPF_REG_0, 1),
+                       BPF_JMP_A(1),
+
+                       /* else return DENY; */
+                       BPF_MOV64_IMM(BPF_REG_0, 0),
+                       BPF_EXIT_INSN(),
+               },
+               .attach_type = BPF_CGROUP_SYSCTL,
+               .sysctl = "net/ipv4/route/mtu_expires",
+               .open_flags = O_RDONLY,
+               .result = SUCCESS,
+       },
+       {
+               "bpf_strtoul negative number, EINVAL",
+               .insns = {
+                       /* arg1 (buf) */
+                       BPF_MOV64_REG(BPF_REG_7, BPF_REG_10),
+                       BPF_ALU64_IMM(BPF_ADD, BPF_REG_7, -8),
+                       BPF_MOV64_IMM(BPF_REG_0, 0x00362d0a), /* " -6\0" */
+                       BPF_STX_MEM(BPF_DW, BPF_REG_7, BPF_REG_0, 0),
+
+                       BPF_MOV64_REG(BPF_REG_1, BPF_REG_7),
+
+                       /* arg2 (buf_len) */
+                       BPF_MOV64_IMM(BPF_REG_2, 4),
+
+                       /* arg3 (flags) */
+                       BPF_MOV64_IMM(BPF_REG_3, 0),
+
+                       /* arg4 (res) */
+                       BPF_ALU64_IMM(BPF_ADD, BPF_REG_7, -8),
+                       BPF_STX_MEM(BPF_DW, BPF_REG_7, BPF_REG_0, 0),
+                       BPF_MOV64_REG(BPF_REG_4, BPF_REG_7),
+
+                       BPF_EMIT_CALL(BPF_FUNC_strtoul),
+
+                       /* if (ret == expected) */
+                       BPF_JMP_IMM(BPF_JNE, BPF_REG_0, -EINVAL, 2),
+
+                       /* return ALLOW; */
+                       BPF_MOV64_IMM(BPF_REG_0, 1),
+                       BPF_JMP_A(1),
+
+                       /* else return DENY; */
+                       BPF_MOV64_IMM(BPF_REG_0, 0),
+                       BPF_EXIT_INSN(),
+               },
+               .attach_type = BPF_CGROUP_SYSCTL,
+               .sysctl = "net/ipv4/route/mtu_expires",
+               .open_flags = O_RDONLY,
+               .result = SUCCESS,
+       },
+       {
+               "bpf_strtol negative number, ok",
+               .insns = {
+                       /* arg1 (buf) */
+                       BPF_MOV64_REG(BPF_REG_7, BPF_REG_10),
+                       BPF_ALU64_IMM(BPF_ADD, BPF_REG_7, -8),
+                       BPF_MOV64_IMM(BPF_REG_0, 0x00362d0a), /* " -6\0" */
+                       BPF_STX_MEM(BPF_DW, BPF_REG_7, BPF_REG_0, 0),
+
+                       BPF_MOV64_REG(BPF_REG_1, BPF_REG_7),
+
+                       /* arg2 (buf_len) */
+                       BPF_MOV64_IMM(BPF_REG_2, 4),
+
+                       /* arg3 (flags) */
+                       BPF_MOV64_IMM(BPF_REG_3, 10),
+
+                       /* arg4 (res) */
+                       BPF_ALU64_IMM(BPF_ADD, BPF_REG_7, -8),
+                       BPF_STX_MEM(BPF_DW, BPF_REG_7, BPF_REG_0, 0),
+                       BPF_MOV64_REG(BPF_REG_4, BPF_REG_7),
+
+                       BPF_EMIT_CALL(BPF_FUNC_strtol),
+
+                       /* if (ret == expected && */
+                       BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 3, 4),
+                       /*     res == expected) */
+                       BPF_LDX_MEM(BPF_DW, BPF_REG_9, BPF_REG_7, 0),
+                       BPF_JMP_IMM(BPF_JNE, BPF_REG_9, -6, 2),
+
+                       /* return ALLOW; */
+                       BPF_MOV64_IMM(BPF_REG_0, 1),
+                       BPF_JMP_A(1),
+
+                       /* else return DENY; */
+                       BPF_MOV64_IMM(BPF_REG_0, 0),
+                       BPF_EXIT_INSN(),
+               },
+               .attach_type = BPF_CGROUP_SYSCTL,
+               .sysctl = "net/ipv4/route/mtu_expires",
+               .open_flags = O_RDONLY,
+               .result = SUCCESS,
+       },
+       {
+               "bpf_strtol hex number, ok",
+               .insns = {
+                       /* arg1 (buf) */
+                       BPF_MOV64_REG(BPF_REG_7, BPF_REG_10),
+                       BPF_ALU64_IMM(BPF_ADD, BPF_REG_7, -8),
+                       BPF_MOV64_IMM(BPF_REG_0, 0x65667830), /* "0xfe" */
+                       BPF_STX_MEM(BPF_DW, BPF_REG_7, BPF_REG_0, 0),
+
+                       BPF_MOV64_REG(BPF_REG_1, BPF_REG_7),
+
+                       /* arg2 (buf_len) */
+                       BPF_MOV64_IMM(BPF_REG_2, 4),
+
+                       /* arg3 (flags) */
+                       BPF_MOV64_IMM(BPF_REG_3, 0),
+
+                       /* arg4 (res) */
+                       BPF_ALU64_IMM(BPF_ADD, BPF_REG_7, -8),
+                       BPF_STX_MEM(BPF_DW, BPF_REG_7, BPF_REG_0, 0),
+                       BPF_MOV64_REG(BPF_REG_4, BPF_REG_7),
+
+                       BPF_EMIT_CALL(BPF_FUNC_strtol),
+
+                       /* if (ret == expected && */
+                       BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 4, 4),
+                       /*     res == expected) */
+                       BPF_LDX_MEM(BPF_DW, BPF_REG_9, BPF_REG_7, 0),
+                       BPF_JMP_IMM(BPF_JNE, BPF_REG_9, 254, 2),
+
+                       /* return ALLOW; */
+                       BPF_MOV64_IMM(BPF_REG_0, 1),
+                       BPF_JMP_A(1),
+
+                       /* else return DENY; */
+                       BPF_MOV64_IMM(BPF_REG_0, 0),
+                       BPF_EXIT_INSN(),
+               },
+               .attach_type = BPF_CGROUP_SYSCTL,
+               .sysctl = "net/ipv4/route/mtu_expires",
+               .open_flags = O_RDONLY,
+               .result = SUCCESS,
+       },
+       {
+               "bpf_strtol max long",
+               .insns = {
+                       /* arg1 (buf) 9223372036854775807 */
+                       BPF_MOV64_REG(BPF_REG_7, BPF_REG_10),
+                       BPF_ALU64_IMM(BPF_ADD, BPF_REG_7, -24),
+                       BPF_LD_IMM64(BPF_REG_0, 0x3032373333323239ULL),
+                       BPF_STX_MEM(BPF_DW, BPF_REG_7, BPF_REG_0, 0),
+                       BPF_LD_IMM64(BPF_REG_0, 0x3537373435383633ULL),
+                       BPF_STX_MEM(BPF_DW, BPF_REG_7, BPF_REG_0, 8),
+                       BPF_LD_IMM64(BPF_REG_0, 0x0000000000373038ULL),
+                       BPF_STX_MEM(BPF_DW, BPF_REG_7, BPF_REG_0, 16),
+
+                       BPF_MOV64_REG(BPF_REG_1, BPF_REG_7),
+
+                       /* arg2 (buf_len) */
+                       BPF_MOV64_IMM(BPF_REG_2, 19),
+
+                       /* arg3 (flags) */
+                       BPF_MOV64_IMM(BPF_REG_3, 0),
+
+                       /* arg4 (res) */
+                       BPF_ALU64_IMM(BPF_ADD, BPF_REG_7, -8),
+                       BPF_STX_MEM(BPF_DW, BPF_REG_7, BPF_REG_0, 0),
+                       BPF_MOV64_REG(BPF_REG_4, BPF_REG_7),
+
+                       BPF_EMIT_CALL(BPF_FUNC_strtol),
+
+                       /* if (ret == expected && */
+                       BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 19, 6),
+                       /*     res == expected) */
+                       BPF_LD_IMM64(BPF_REG_8, 0x7fffffffffffffffULL),
+                       BPF_LDX_MEM(BPF_DW, BPF_REG_9, BPF_REG_7, 0),
+                       BPF_JMP_REG(BPF_JNE, BPF_REG_8, BPF_REG_9, 2),
+
+                       /* return ALLOW; */
+                       BPF_MOV64_IMM(BPF_REG_0, 1),
+                       BPF_JMP_A(1),
+
+                       /* else return DENY; */
+                       BPF_MOV64_IMM(BPF_REG_0, 0),
+                       BPF_EXIT_INSN(),
+               },
+               .attach_type = BPF_CGROUP_SYSCTL,
+               .sysctl = "net/ipv4/route/mtu_expires",
+               .open_flags = O_RDONLY,
+               .result = SUCCESS,
+       },
+       {
+               "bpf_strtol overflow, ERANGE",
+               .insns = {
+                       /* arg1 (buf) 9223372036854775808 */
+                       BPF_MOV64_REG(BPF_REG_7, BPF_REG_10),
+                       BPF_ALU64_IMM(BPF_ADD, BPF_REG_7, -24),
+                       BPF_LD_IMM64(BPF_REG_0, 0x3032373333323239ULL),
+                       BPF_STX_MEM(BPF_DW, BPF_REG_7, BPF_REG_0, 0),
+                       BPF_LD_IMM64(BPF_REG_0, 0x3537373435383633ULL),
+                       BPF_STX_MEM(BPF_DW, BPF_REG_7, BPF_REG_0, 8),
+                       BPF_LD_IMM64(BPF_REG_0, 0x0000000000383038ULL),
+                       BPF_STX_MEM(BPF_DW, BPF_REG_7, BPF_REG_0, 16),
+
+                       BPF_MOV64_REG(BPF_REG_1, BPF_REG_7),
+
+                       /* arg2 (buf_len) */
+                       BPF_MOV64_IMM(BPF_REG_2, 19),
+
+                       /* arg3 (flags) */
+                       BPF_MOV64_IMM(BPF_REG_3, 0),
+
+                       /* arg4 (res) */
+                       BPF_ALU64_IMM(BPF_ADD, BPF_REG_7, -8),
+                       BPF_STX_MEM(BPF_DW, BPF_REG_7, BPF_REG_0, 0),
+                       BPF_MOV64_REG(BPF_REG_4, BPF_REG_7),
+
+                       BPF_EMIT_CALL(BPF_FUNC_strtol),
+
+                       /* if (ret == expected) */
+                       BPF_JMP_IMM(BPF_JNE, BPF_REG_0, -ERANGE, 2),
+
+                       /* return ALLOW; */
+                       BPF_MOV64_IMM(BPF_REG_0, 1),
+                       BPF_JMP_A(1),
+
+                       /* else return DENY; */
+                       BPF_MOV64_IMM(BPF_REG_0, 0),
+                       BPF_EXIT_INSN(),
+               },
+               .attach_type = BPF_CGROUP_SYSCTL,
+               .sysctl = "net/ipv4/route/mtu_expires",
+               .open_flags = O_RDONLY,
+               .result = SUCCESS,
+       },
 };
 
 static size_t probe_prog_length(const struct bpf_insn *fp)