selftests/bpf: C based test for sysctl and strtoX

Add C based test for a few bpf_sysctl_* helpers and bpf_strtoul.

Make sure that sysctl can be identified by name and that multiple
integers can be parsed from sysctl value with bpf_strtoul.

net/ipv4/tcp_mem is chosen as a testing sysctl, it contains 3 unsigned
longs, they all are parsed and compared (val[0] < val[1] < val[2]).

Example of output:
  # ./test_sysctl
  ...
  Test case: C prog: deny all writes .. [PASS]
  Test case: C prog: deny access by name .. [PASS]
  Test case: C prog: read tcp_mem .. [PASS]
  Summary: 39 PASSED, 0 FAILED

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

1 files changed, 70 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/progs/test_sysctl_prog.c b/tools/testing/selftests/bpf/progs/test_sysctl_prog.c
new file mode 100644
index 000000000000..a295cad805d7
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_sysctl_prog.c
@@ -0,0 +1,70 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (c) 2019 Facebook
+
+#include <stdint.h>
+#include <string.h>
+
+#include <linux/stddef.h>
+#include <linux/bpf.h>
+
+#include "bpf_helpers.h"
+#include "bpf_util.h"
+
+/* Max supported length of a string with unsigned long in base 10 (pow2 - 1). */
+#define MAX_ULONG_STR_LEN 0xF
+
+/* Max supported length of sysctl value string (pow2). */
+#define MAX_VALUE_STR_LEN 0x40
+
+static __always_inline int is_tcp_mem(struct bpf_sysctl *ctx)
+{
+	char tcp_mem_name[] = "net/ipv4/tcp_mem";
+	unsigned char i;
+	char name[64];
+	int ret;
+
+	memset(name, 0, sizeof(name));
+	ret = bpf_sysctl_get_name(ctx, name, sizeof(name), 0);
+	if (ret < 0 || ret != sizeof(tcp_mem_name) - 1)
+		return 0;
+
+#pragma clang loop unroll(full)
+	for (i = 0; i < sizeof(tcp_mem_name); ++i)
+		if (name[i] != tcp_mem_name[i])
+			return 0;
+
+	return 1;
+}
+
+SEC("cgroup/sysctl")
+int sysctl_tcp_mem(struct bpf_sysctl *ctx)
+{
+	unsigned long tcp_mem[3] = {0, 0, 0};
+	char value[MAX_VALUE_STR_LEN];
+	unsigned char i, off = 0;
+	int ret;
+
+	if (ctx->write)
+		return 0;
+
+	if (!is_tcp_mem(ctx))
+		return 0;
+
+	ret = bpf_sysctl_get_current_value(ctx, value, MAX_VALUE_STR_LEN);
+	if (ret < 0 || ret >= MAX_VALUE_STR_LEN)
+		return 0;
+
+#pragma clang loop unroll(full)
+	for (i = 0; i < ARRAY_SIZE(tcp_mem); ++i) {
+		ret = bpf_strtoul(value + off, MAX_ULONG_STR_LEN, 0,
+				  tcp_mem + i);
+		if (ret <= 0 || ret > MAX_ULONG_STR_LEN)
+			return 0;
+		off += ret & MAX_ULONG_STR_LEN;
+	}
+
+
+	return tcp_mem[0] < tcp_mem[1] && tcp_mem[1] < tcp_mem[2];
+}
+
+char _license[] SEC("license") = "GPL";