selftests/bpf: Add a series of tests for bpf_snprintf

The "positive" part tests all format specifiers when things go well.

The "negative" part makes sure that incorrect format strings fail at
load time.
Signed-off-by: Florent Revest <revest@chromium.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210419155243.1632274-7-revest@chromium.org

tools/testing/selftests/bpf/prog_tests/snprintf.c

+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Google LLC. */
+
+#include <test_progs.h>
+#include "test_snprintf.skel.h"
+#include "test_snprintf_single.skel.h"
+
+#define EXP_NUM_OUT  "-8 9 96 -424242 1337 DABBAD00"
+#define EXP_NUM_RET  sizeof(EXP_NUM_OUT)
+
+#define EXP_IP_OUT   "127.000.000.001 0000:0000:0000:0000:0000:0000:0000:0001"
+#define EXP_IP_RET   sizeof(EXP_IP_OUT)
+
+/* The third specifier, %pB, depends on compiler inlining so don't check it */
+#define EXP_SYM_OUT  "schedule schedule+0x0/"
+#define MIN_SYM_RET  sizeof(EXP_SYM_OUT)
+
+/* The third specifier, %p, is a hashed pointer which changes on every reboot */
+#define EXP_ADDR_OUT "0000000000000000 ffff00000add4e55 "
+#define EXP_ADDR_RET sizeof(EXP_ADDR_OUT "unknownhashedptr")
+
+#define EXP_STR_OUT  "str1 longstr"
+#define EXP_STR_RET  sizeof(EXP_STR_OUT)
+
+#define EXP_OVER_OUT "%over"
+#define EXP_OVER_RET 10
+
+#define EXP_PAD_OUT "    4 000"
+#define EXP_PAD_RET 900007
+
+#define EXP_NO_ARG_OUT "simple case"
+#define EXP_NO_ARG_RET 12
+
+#define EXP_NO_BUF_RET 29
+
+void test_snprintf_positive(void)
+{
+	char exp_addr_out[] = EXP_ADDR_OUT;
+	char exp_sym_out[]  = EXP_SYM_OUT;
+	struct test_snprintf *skel;
+
+	skel = test_snprintf__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "skel_open"))
+		return;
+
+	if (!ASSERT_OK(test_snprintf__attach(skel), "skel_attach"))
+		goto cleanup;
+
+	/* trigger tracepoint */
+	usleep(1);
+
+	ASSERT_STREQ(skel->bss->num_out, EXP_NUM_OUT, "num_out");
+	ASSERT_EQ(skel->bss->num_ret, EXP_NUM_RET, "num_ret");
+
+	ASSERT_STREQ(skel->bss->ip_out, EXP_IP_OUT, "ip_out");
+	ASSERT_EQ(skel->bss->ip_ret, EXP_IP_RET, "ip_ret");
+
+	ASSERT_OK(memcmp(skel->bss->sym_out, exp_sym_out,
+			 sizeof(exp_sym_out) - 1), "sym_out");
+	ASSERT_LT(MIN_SYM_RET, skel->bss->sym_ret, "sym_ret");
+
+	ASSERT_OK(memcmp(skel->bss->addr_out, exp_addr_out,
+			 sizeof(exp_addr_out) - 1), "addr_out");
+	ASSERT_EQ(skel->bss->addr_ret, EXP_ADDR_RET, "addr_ret");
+
+	ASSERT_STREQ(skel->bss->str_out, EXP_STR_OUT, "str_out");
+	ASSERT_EQ(skel->bss->str_ret, EXP_STR_RET, "str_ret");
+
+	ASSERT_STREQ(skel->bss->over_out, EXP_OVER_OUT, "over_out");
+	ASSERT_EQ(skel->bss->over_ret, EXP_OVER_RET, "over_ret");
+
+	ASSERT_STREQ(skel->bss->pad_out, EXP_PAD_OUT, "pad_out");
+	ASSERT_EQ(skel->bss->pad_ret, EXP_PAD_RET, "pad_ret");
+
+	ASSERT_STREQ(skel->bss->noarg_out, EXP_NO_ARG_OUT, "no_arg_out");
+	ASSERT_EQ(skel->bss->noarg_ret, EXP_NO_ARG_RET, "no_arg_ret");
+
+	ASSERT_EQ(skel->bss->nobuf_ret, EXP_NO_BUF_RET, "no_buf_ret");
+
+cleanup:
+	test_snprintf__destroy(skel);
+}
+
+#define min(a, b) ((a) < (b) ? (a) : (b))
+
+/* Loads an eBPF object calling bpf_snprintf with up to 10 characters of fmt */
+static int load_single_snprintf(char *fmt)
+{
+	struct test_snprintf_single *skel;
+	int ret;
+
+	skel = test_snprintf_single__open();
+	if (!skel)
+		return -EINVAL;
+
+	memcpy(skel->rodata->fmt, fmt, min(strlen(fmt) + 1, 10));
+
+	ret = test_snprintf_single__load(skel);
+	test_snprintf_single__destroy(skel);
+
+	return ret;
+}
+
+void test_snprintf_negative(void)
+{
+	ASSERT_OK(load_single_snprintf("valid %d"), "valid usage");
+
+	ASSERT_ERR(load_single_snprintf("0123456789"), "no terminating zero");
+	ASSERT_ERR(load_single_snprintf("%d %d"), "too many specifiers");
+	ASSERT_ERR(load_single_snprintf("%pi5"), "invalid specifier 1");
+	ASSERT_ERR(load_single_snprintf("%a"), "invalid specifier 2");
+	ASSERT_ERR(load_single_snprintf("%"), "invalid specifier 3");
+	ASSERT_ERR(load_single_snprintf("%12345678"), "invalid specifier 4");
+	ASSERT_ERR(load_single_snprintf("%--------"), "invalid specifier 5");
+	ASSERT_ERR(load_single_snprintf("\x80"), "non ascii character");
+	ASSERT_ERR(load_single_snprintf("\x1"), "non printable character");
+}
+
+void test_snprintf(void)
+{
+	if (test__start_subtest("snprintf_positive"))
+		test_snprintf_positive();
+	if (test__start_subtest("snprintf_negative"))
+		test_snprintf_negative();
+}

tools/testing/selftests/bpf/progs/test_snprintf.c

+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Google LLC. */
+
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+char num_out[64] = {};
+long num_ret = 0;
+
+char ip_out[64] = {};
+long ip_ret = 0;
+
+char sym_out[64] = {};
+long sym_ret = 0;
+
+char addr_out[64] = {};
+long addr_ret = 0;
+
+char str_out[64] = {};
+long str_ret = 0;
+
+char over_out[6] = {};
+long over_ret = 0;
+
+char pad_out[10] = {};
+long pad_ret = 0;
+
+char noarg_out[64] = {};
+long noarg_ret = 0;
+
+long nobuf_ret = 0;
+
+extern const void schedule __ksym;
+
+SEC("raw_tp/sys_enter")
+int handler(const void *ctx)
+{
+	/* Convenient values to pretty-print */
+	const __u8 ex_ipv4[] = {127, 0, 0, 1};
+	const __u8 ex_ipv6[] = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1};
+	static const char str1[] = "str1";
+	static const char longstr[] = "longstr";
+
+	/* Integer types */
+	num_ret  = BPF_SNPRINTF(num_out, sizeof(num_out),
+				"%d %u %x %li %llu %lX",
+				-8, 9, 150, -424242, 1337, 0xDABBAD00);
+	/* IP addresses */
+	ip_ret   = BPF_SNPRINTF(ip_out, sizeof(ip_out), "%pi4 %pI6",
+				&ex_ipv4, &ex_ipv6);
+	/* Symbol lookup formatting */
+	sym_ret  = BPF_SNPRINTF(sym_out,  sizeof(sym_out), "%ps %pS %pB",
+				&schedule, &schedule, &schedule);
+	/* Kernel pointers */
+	addr_ret = BPF_SNPRINTF(addr_out, sizeof(addr_out), "%pK %px %p",
+				0, 0xFFFF00000ADD4E55, 0xFFFF00000ADD4E55);
+	/* Strings embedding */
+	str_ret  = BPF_SNPRINTF(str_out, sizeof(str_out), "%s %+05s",
+				str1, longstr);
+	/* Overflow */
+	over_ret = BPF_SNPRINTF(over_out, sizeof(over_out), "%%overflow");
+	/* Padding of fixed width numbers */
+	pad_ret = BPF_SNPRINTF(pad_out, sizeof(pad_out), "%5d %0900000X", 4, 4);
+	/* No args */
+	noarg_ret = BPF_SNPRINTF(noarg_out, sizeof(noarg_out), "simple case");
+	/* No buffer */
+	nobuf_ret = BPF_SNPRINTF(NULL, 0, "only interested in length %d", 60);
+
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";

tools/testing/selftests/bpf/progs/test_snprintf_single.c

+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Google LLC. */
+
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+
+/* The format string is filled from the userspace such that loading fails */
+static const char fmt[10];
+
+SEC("raw_tp/sys_enter")
+int handler(const void *ctx)
+{
+	unsigned long long arg = 42;
+
+	bpf_snprintf(NULL, 0, fmt, &arg, sizeof(arg));
+
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";