new file mode 100644
@@ -0,0 +1,89 @@
+// 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"
+
+/* Min/max supported lengths of a string with unsigned long in base 10. */
+#define MIN_ULONG_STR_LEN 2
+#define MAX_ULONG_STR_LEN 15
+
+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 mem_min = 0, mem_pressure = 0, mem_max = 0;
+ unsigned char i, off;
+ char value[64];
+ int ret;
+
+ if (ctx->write)
+ return 0;
+
+ if (!is_tcp_mem(ctx))
+ return 0;
+
+ ret = bpf_sysctl_get_current_value(ctx, value, sizeof(value));
+ if (ret < 0 || ret >= sizeof(value))
+ return 0;
+
+ ret = bpf_strtoul(value, sizeof(value), 0, &mem_min);
+ if (ret <= 0 || ret > MAX_ULONG_STR_LEN)
+ return 0;
+ off = ret;
+ ret = -1;
+
+ /* Make verifier happy, prevent "invalid variable stack read R1
+ * var_off=(0x0; 0xf)" by using static offset for value.
+ */
+#pragma clang loop unroll(full)
+ for (i = MIN_ULONG_STR_LEN; i <= MAX_ULONG_STR_LEN; ++i)
+ if (off == i) {
+ ret = bpf_strtoul(value + i, sizeof(value) - i, 0,
+ &mem_pressure);
+ break;
+ }
+ if (ret <= 0 || ret > MAX_ULONG_STR_LEN)
+ return 0;
+ off += ret;
+ ret = -1;
+
+ /* Same here. */
+#pragma clang loop unroll(full)
+ for (i = MIN_ULONG_STR_LEN * 2; i <= MAX_ULONG_STR_LEN * 2 + 2; ++i)
+ if (off == i) {
+ ret = bpf_strtoul(value + i, sizeof(value) - i, 0,
+ &mem_max);
+ break;
+ }
+ if (ret <= 0 || ret > MAX_ULONG_STR_LEN)
+ return 0;
+
+ return mem_min < mem_pressure && mem_pressure < mem_max;
+}
+
+char _license[] SEC("license") = "GPL";
@@ -11,6 +11,7 @@
#include <linux/filter.h>
#include <bpf/bpf.h>
+#include <bpf/libbpf.h>
#include "bpf_rlimit.h"
#include "bpf_util.h"
@@ -26,6 +27,7 @@ struct sysctl_test {
const char *descr;
size_t fixup_value_insn;
struct bpf_insn insns[MAX_INSNS];
+ const char *prog_file;
enum bpf_attach_type attach_type;
const char *sysctl;
int open_flags;
@@ -1302,6 +1304,31 @@ static struct sysctl_test tests[] = {
.open_flags = O_RDONLY,
.result = SUCCESS,
},
+ {
+ "C prog: deny all writes",
+ .prog_file = "./test_sysctl_prog.o",
+ .attach_type = BPF_CGROUP_SYSCTL,
+ .sysctl = "net/ipv4/tcp_mem",
+ .open_flags = O_WRONLY,
+ .newval = "123 456 789",
+ .result = OP_EPERM,
+ },
+ {
+ "C prog: deny access by name",
+ .prog_file = "./test_sysctl_prog.o",
+ .attach_type = BPF_CGROUP_SYSCTL,
+ .sysctl = "net/ipv4/route/mtu_expires",
+ .open_flags = O_RDONLY,
+ .result = OP_EPERM,
+ },
+ {
+ "C prog: read tcp_mem",
+ .prog_file = "./test_sysctl_prog.o",
+ .attach_type = BPF_CGROUP_SYSCTL,
+ .sysctl = "net/ipv4/tcp_mem",
+ .open_flags = O_RDONLY,
+ .result = SUCCESS,
+ },
};
static size_t probe_prog_length(const struct bpf_insn *fp)
@@ -1335,7 +1362,8 @@ static int fixup_sysctl_value(const char *buf, size_t buf_len,
return 0;
}
-static int load_sysctl_prog(struct sysctl_test *test, const char *sysctl_path)
+static int load_sysctl_prog_insns(struct sysctl_test *test,
+ const char *sysctl_path)
{
struct bpf_insn *prog = test->insns;
struct bpf_load_program_attr attr;
@@ -1377,6 +1405,33 @@ static int load_sysctl_prog(struct sysctl_test *test, const char *sysctl_path)
return ret;
}
+static int load_sysctl_prog_file(struct sysctl_test *test)
+{
+ struct bpf_prog_load_attr attr;
+ struct bpf_object *obj;
+ int prog_fd;
+
+ memset(&attr, 0, sizeof(struct bpf_prog_load_attr));
+ attr.file = test->prog_file;
+ attr.prog_type = BPF_PROG_TYPE_CGROUP_SYSCTL;
+
+ if (bpf_prog_load_xattr(&attr, &obj, &prog_fd)) {
+ if (test->result != LOAD_REJECT)
+ log_err(">>> Loading program (%s) error.\n",
+ test->prog_file);
+ return -1;
+ }
+
+ return prog_fd;
+}
+
+static int load_sysctl_prog(struct sysctl_test *test, const char *sysctl_path)
+{
+ return test->prog_file
+ ? load_sysctl_prog_file(test)
+ : load_sysctl_prog_insns(test, sysctl_path);
+}
+
static int access_sysctl(const char *sysctl_path,
const struct sysctl_test *test)
{
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]). One verifier limitation is being worked around in the test: variable stack access. Since such an access is unsupported, offset, returned by bpf_strtoul while parsing current ulong, can't be used directly when specifying 'buf' pointer to the next bpf_strtoul. That's why instead of 'base + offset' where offset non-const tnum, the test uses brute force search to find static number, that matches with 'offset', and use 'base + static' to access the stack. 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> --- .../selftests/bpf/progs/test_sysctl_prog.c | 89 +++++++++++++++++++ tools/testing/selftests/bpf/test_sysctl.c | 57 +++++++++++- 2 files changed, 145 insertions(+), 1 deletion(-) create mode 100644 tools/testing/selftests/bpf/progs/test_sysctl_prog.c