selftest/bpf: Test bpf_probe_read_user_str() strips trailing bytes after NUL

// SPDX-License-Identifier: GPL-2.0

#include <test_progs.h>

#include "test_probe_read_user_str.skel.h"

static const char str1[] = "mestring";

static const char str2[] = "mestringalittlebigger";

static const char str3[] = "mestringblubblubblubblubblub";

static int test_one_str(struct test_probe_read_user_str *skel, const char *str,

			size_t len)

{

	int err, duration = 0;

	char buf[256];

	/* Ensure bytes after string are ones */

	memset(buf, 1, sizeof(buf));

	memcpy(buf, str, len);

	/* Give prog our userspace pointer */

	skel->bss->user_ptr = buf;

	/* Trigger tracepoint */

	usleep(1);

	/* Did helper fail? */

	if (CHECK(skel->bss->ret < 0, "prog_ret", "prog returned: %ld\n",

		  skel->bss->ret))

		return 1;

	/* Check that string was copied correctly */

	err = memcmp(skel->bss->buf, str, len);

	if (CHECK(err, "memcmp", "prog copied wrong string"))

		return 1;

	/* Now check that no extra trailing bytes were copied */

	memset(buf, 0, sizeof(buf));

	err = memcmp(skel->bss->buf + len, buf, sizeof(buf) - len);

	if (CHECK(err, "memcmp", "trailing bytes were not stripped"))

		return 1;

	return 0;

}

void test_probe_read_user_str(void)

{

	struct test_probe_read_user_str *skel;

	int err, duration = 0;

	skel = test_probe_read_user_str__open_and_load();

	if (CHECK(!skel, "test_probe_read_user_str__open_and_load",

		  "skeleton open and load failed\n"))

		return;

	/* Give pid to bpf prog so it doesn't read from anyone else */

	skel->bss->pid = getpid();

	err = test_probe_read_user_str__attach(skel);

	if (CHECK(err, "test_probe_read_user_str__attach",

		  "skeleton attach failed: %d\n", err))

		goto out;

	if (test_one_str(skel, str1, sizeof(str1)))

		goto out;

	if (test_one_str(skel, str2, sizeof(str2)))

		goto out;

	if (test_one_str(skel, str3, sizeof(str3)))

		goto out;

out:

	test_probe_read_user_str__destroy(skel);

}

// SPDX-License-Identifier: GPL-2.0

#include <linux/bpf.h>

#include <bpf/bpf_helpers.h>

#include <bpf/bpf_tracing.h>

#include <sys/types.h>

pid_t pid = 0;

long ret = 0;

void *user_ptr = 0;

char buf[256] = {};

SEC("tracepoint/syscalls/sys_enter_nanosleep")

int on_write(void *ctx)

{

	if (pid != (bpf_get_current_pid_tgid() >> 32))

		return 0;

	ret = bpf_probe_read_user_str(buf, sizeof(buf), user_ptr);

	return 0;

}

char _license[] SEC("license") = "GPL";