selftests/bpf: Add test cases for bpf_strncmp()

Four test cases are added:
(1) ensure the return value is expected
(2) ensure no const string size is rejected
(3) ensure writable target is rejected
(4) ensure no null-terminated target is rejected

Signed-off-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211210141652.877186-5-houtao1@huawei.com

diff --git a/tools/testing/selftests/bpf/prog_tests/test_strncmp.c b/tools/testing/selftests/bpf/prog_tests/test_strncmp.c
new file mode 100644 (file)
index 0000000..b57a300
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/test_strncmp.c
@@ -0,0 +1,167 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (C) 2021. Huawei Technologies Co., Ltd */
+#include <test_progs.h>
+#include "strncmp_test.skel.h"
+
+static int trigger_strncmp(const struct strncmp_test *skel)
+{
+       int cmp;
+
+       usleep(1);
+
+       cmp = skel->bss->cmp_ret;
+       if (cmp > 0)
+               return 1;
+       if (cmp < 0)
+               return -1;
+       return 0;
+}
+
+/*
+ * Compare str and target after making str[i] != target[i].
+ * When exp is -1, make str[i] < target[i] and delta = -1.
+ */
+static void strncmp_full_str_cmp(struct strncmp_test *skel, const char *name,
+                                int exp)
+{
+       size_t nr = sizeof(skel->bss->str);
+       char *str = skel->bss->str;
+       int delta = exp;
+       int got;
+       size_t i;
+
+       memcpy(str, skel->rodata->target, nr);
+       for (i = 0; i < nr - 1; i++) {
+               str[i] += delta;
+
+               got = trigger_strncmp(skel);
+               ASSERT_EQ(got, exp, name);
+
+               str[i] -= delta;
+       }
+}
+
+static void test_strncmp_ret(void)
+{
+       struct strncmp_test *skel;
+       struct bpf_program *prog;
+       int err, got;
+
+       skel = strncmp_test__open();
+       if (!ASSERT_OK_PTR(skel, "strncmp_test open"))
+               return;
+
+       bpf_object__for_each_program(prog, skel->obj)
+               bpf_program__set_autoload(prog, false);
+
+       bpf_program__set_autoload(skel->progs.do_strncmp, true);
+
+       err = strncmp_test__load(skel);
+       if (!ASSERT_EQ(err, 0, "strncmp_test load"))
+               goto out;
+
+       err = strncmp_test__attach(skel);
+       if (!ASSERT_EQ(err, 0, "strncmp_test attach"))
+               goto out;
+
+       skel->bss->target_pid = getpid();
+
+       /* Empty str */
+       skel->bss->str[0] = '\0';
+       got = trigger_strncmp(skel);
+       ASSERT_EQ(got, -1, "strncmp: empty str");
+
+       /* Same string */
+       memcpy(skel->bss->str, skel->rodata->target, sizeof(skel->bss->str));
+       got = trigger_strncmp(skel);
+       ASSERT_EQ(got, 0, "strncmp: same str");
+
+       /* Not-null-termainted string  */
+       memcpy(skel->bss->str, skel->rodata->target, sizeof(skel->bss->str));
+       skel->bss->str[sizeof(skel->bss->str) - 1] = 'A';
+       got = trigger_strncmp(skel);
+       ASSERT_EQ(got, 1, "strncmp: not-null-term str");
+
+       strncmp_full_str_cmp(skel, "strncmp: less than", -1);
+       strncmp_full_str_cmp(skel, "strncmp: greater than", 1);
+out:
+       strncmp_test__destroy(skel);
+}
+
+static void test_strncmp_bad_not_const_str_size(void)
+{
+       struct strncmp_test *skel;
+       struct bpf_program *prog;
+       int err;
+
+       skel = strncmp_test__open();
+       if (!ASSERT_OK_PTR(skel, "strncmp_test open"))
+               return;
+
+       bpf_object__for_each_program(prog, skel->obj)
+               bpf_program__set_autoload(prog, false);
+
+       bpf_program__set_autoload(skel->progs.strncmp_bad_not_const_str_size,
+                                 true);
+
+       err = strncmp_test__load(skel);
+       ASSERT_ERR(err, "strncmp_test load bad_not_const_str_size");
+
+       strncmp_test__destroy(skel);
+}
+
+static void test_strncmp_bad_writable_target(void)
+{
+       struct strncmp_test *skel;
+       struct bpf_program *prog;
+       int err;
+
+       skel = strncmp_test__open();
+       if (!ASSERT_OK_PTR(skel, "strncmp_test open"))
+               return;
+
+       bpf_object__for_each_program(prog, skel->obj)
+               bpf_program__set_autoload(prog, false);
+
+       bpf_program__set_autoload(skel->progs.strncmp_bad_writable_target,
+                                 true);
+
+       err = strncmp_test__load(skel);
+       ASSERT_ERR(err, "strncmp_test load bad_writable_target");
+
+       strncmp_test__destroy(skel);
+}
+
+static void test_strncmp_bad_not_null_term_target(void)
+{
+       struct strncmp_test *skel;
+       struct bpf_program *prog;
+       int err;
+
+       skel = strncmp_test__open();
+       if (!ASSERT_OK_PTR(skel, "strncmp_test open"))
+               return;
+
+       bpf_object__for_each_program(prog, skel->obj)
+               bpf_program__set_autoload(prog, false);
+
+       bpf_program__set_autoload(skel->progs.strncmp_bad_not_null_term_target,
+                                 true);
+
+       err = strncmp_test__load(skel);
+       ASSERT_ERR(err, "strncmp_test load bad_not_null_term_target");
+
+       strncmp_test__destroy(skel);
+}
+
+void test_test_strncmp(void)
+{
+       if (test__start_subtest("strncmp_ret"))
+               test_strncmp_ret();
+       if (test__start_subtest("strncmp_bad_not_const_str_size"))
+               test_strncmp_bad_not_const_str_size();
+       if (test__start_subtest("strncmp_bad_writable_target"))
+               test_strncmp_bad_writable_target();
+       if (test__start_subtest("strncmp_bad_not_null_term_target"))
+               test_strncmp_bad_not_null_term_target();
+}

diff --git a/tools/testing/selftests/bpf/progs/strncmp_test.c b/tools/testing/selftests/bpf/progs/strncmp_test.c
new file mode 100644 (file)
index 0000000..900d930
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/strncmp_test.c
@@ -0,0 +1,54 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (C) 2021. Huawei Technologies Co., Ltd */
+#include <stdbool.h>
+#include <linux/types.h>
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+#define STRNCMP_STR_SZ 8
+
+const char target[STRNCMP_STR_SZ] = "EEEEEEE";
+char str[STRNCMP_STR_SZ];
+int cmp_ret = 0;
+int target_pid = 0;
+
+const char no_str_target[STRNCMP_STR_SZ] = "12345678";
+char writable_target[STRNCMP_STR_SZ];
+unsigned int no_const_str_size = STRNCMP_STR_SZ;
+
+char _license[] SEC("license") = "GPL";
+
+SEC("tp/syscalls/sys_enter_nanosleep")
+int do_strncmp(void *ctx)
+{
+       if ((bpf_get_current_pid_tgid() >> 32) != target_pid)
+               return 0;
+
+       cmp_ret = bpf_strncmp(str, STRNCMP_STR_SZ, target);
+       return 0;
+}
+
+SEC("tp/syscalls/sys_enter_nanosleep")
+int strncmp_bad_not_const_str_size(void *ctx)
+{
+       /* The value of string size is not const, so will fail */
+       cmp_ret = bpf_strncmp(str, no_const_str_size, target);
+       return 0;
+}
+
+SEC("tp/syscalls/sys_enter_nanosleep")
+int strncmp_bad_writable_target(void *ctx)
+{
+       /* Compared target is not read-only, so will fail */
+       cmp_ret = bpf_strncmp(str, STRNCMP_STR_SZ, writable_target);
+       return 0;
+}
+
+SEC("tp/syscalls/sys_enter_nanosleep")
+int strncmp_bad_not_null_term_target(void *ctx)
+{
+       /* Compared target is not null-terminated, so will fail */
+       cmp_ret = bpf_strncmp(str, STRNCMP_STR_SZ, no_str_target);
+       return 0;
+}