test-bpf-devices: new test for the devices bpf code

src/core/bpf-devices.c

@@ -172,14 +172,14 @@ int bpf_devices_apply_policy(
                 bool whitelist,
                 const char *cgroup_path,
                 BPFProgram **prog_installed) {
+
+        _cleanup_free_ char *controller_path = NULL;
         int r;
 
         /* This will assign *keep_program if everything goes well. */
-        if (!prog) {
-                /* Remove existing program. */
-                *prog_installed = bpf_program_unref(*prog_installed);
-                return 0;
-        }
+
+        if (!prog)
+                goto finish;
 
         const bool deny_everything = policy == CGROUP_DEVICE_POLICY_STRICT && !whitelist;
 
@@ -213,7 +213,6 @@ int bpf_devices_apply_policy(
         if (r < 0)
                 return log_error_errno(r, "Extending device control BPF program failed: %m");
 
-        _cleanup_free_ char *controller_path = NULL;
         r = cg_get_path(SYSTEMD_CGROUP_CONTROLLER, cgroup_path, NULL, &controller_path);
         if (r < 0)
                 return log_error_errno(r, "Failed to determine cgroup path: %m");
@@ -223,9 +222,12 @@ int bpf_devices_apply_policy(
                 return log_error_errno(r, "Attaching device control BPF program to cgroup %s failed: %m",
                                        cgroup_path);
 
+ finish:
         /* Unref the old BPF program (which will implicitly detach it) right before attaching the new program. */
-        bpf_program_unref(*prog_installed);
-        *prog_installed = bpf_program_ref(prog);
+        if (prog_installed) {
+                bpf_program_unref(*prog_installed);
+                *prog_installed = bpf_program_ref(prog);
+        }
         return 0;
 }
 

src/test/meson.build

@@ -425,6 +425,16 @@ tests += [
          [libbasic],
          []],
 
+        [['src/test/test-bpf-devices.c'],
+         [libcore,
+          libshared],
+         [libmount,
+          threads,
+          librt,
+          libseccomp,
+          libselinux,
+          libblkid]],
+
         [['src/test/test-bpf-firewall.c'],
          [libcore,
           libshared],

src/test/test-bpf-devices.c

@@ -0,0 +1,268 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+
+#include <sys/resource.h>
+#include <sys/time.h>
+#include <unistd.h>
+
+#include "alloc-util.h"
+#include "bpf-devices.h"
+#include "bpf-program.h"
+#include "cgroup-setup.h"
+#include "errno-list.h"
+#include "fd-util.h"
+#include "fs-util.h"
+#include "path-util.h"
+#include "tests.h"
+
+static void test_policy_closed(const char *cgroup_path, BPFProgram **installed_prog) {
+        _cleanup_(bpf_program_unrefp) BPFProgram *prog = NULL;
+        unsigned wrong = 0;
+        int r;
+
+        log_info("/* %s */", __func__);
+
+        r = bpf_devices_cgroup_init(&prog, CGROUP_DEVICE_POLICY_CLOSED, true);
+        assert_se(r >= 0);
+
+        r = bpf_devices_whitelist_static(prog, cgroup_path);
+        assert_se(r >= 0);
+
+        r = bpf_devices_apply_policy(prog, CGROUP_DEVICE_POLICY_CLOSED, true, cgroup_path, installed_prog);
+        assert_se(r >= 0);
+
+        const char *s;
+        FOREACH_STRING(s, "/dev/null",
+                          "/dev/zero",
+                          "/dev/full",
+                          "/dev/random",
+                          "/dev/urandom",
+                          "/dev/tty",
+                          "/dev/ptmx") {
+                _cleanup_close_ int fd, fd2;
+
+                fd = open(s, O_CLOEXEC|O_RDONLY|O_NOCTTY);
+                log_debug("open(%s, \"r\") = %d/%s", s, fd, fd < 0 ? errno_to_name(errno) : "-");
+                wrong += fd < 0 && errno == EPERM;
+                /* We ignore errors other than EPERM, e.g. ENOENT or ENXIO */
+
+                fd2 = open(s, O_CLOEXEC|O_WRONLY|O_NOCTTY);
+                log_debug("open(%s, \"w\") = %d/%s", s, fd2, fd2 < 0 ? errno_to_name(errno) : "-");
+                wrong += fd2 < 0 && errno == EPERM;
+        }
+        assert_se(wrong == 0);
+}
+
+static void test_policy_strict(const char *cgroup_path, BPFProgram **installed_prog) {
+        _cleanup_(bpf_program_unrefp) BPFProgram *prog = NULL;
+        unsigned wrong = 0;
+        int r;
+
+        log_info("/* %s */", __func__);
+
+        r = bpf_devices_cgroup_init(&prog, CGROUP_DEVICE_POLICY_STRICT, true);
+        assert_se(r >= 0);
+
+        r = bpf_devices_whitelist_device(prog, cgroup_path, "/dev/null", "rw");
+        assert_se(r >= 0);
+
+        r = bpf_devices_whitelist_device(prog, cgroup_path, "/dev/random", "r");
+        assert_se(r >= 0);
+
+        r = bpf_devices_whitelist_device(prog, cgroup_path, "/dev/zero", "w");
+        assert_se(r >= 0);
+
+        r = bpf_devices_apply_policy(prog, CGROUP_DEVICE_POLICY_STRICT, true, cgroup_path, installed_prog);
+        assert_se(r >= 0);
+
+        {
+                _cleanup_close_ int fd, fd2;
+                const char *s = "/dev/null";
+
+                fd = open(s, O_CLOEXEC|O_RDONLY|O_NOCTTY);
+                log_debug("open(%s, \"r\") = %d/%s", s, fd, fd < 0 ? errno_to_name(errno) : "-");
+                wrong += fd < 0;
+
+                fd2 = open(s, O_CLOEXEC|O_WRONLY|O_NOCTTY);
+                log_debug("open(%s, \"w\") = %d/%s", s, fd2, fd2 < 0 ? errno_to_name(errno) : "-");
+                wrong += fd2 < 0;
+        }
+
+        {
+                _cleanup_close_ int fd, fd2;
+                const char *s = "/dev/random";
+
+                fd = open(s, O_CLOEXEC|O_RDONLY|O_NOCTTY);
+                log_debug("open(%s, \"r\") = %d/%s", s, fd, fd < 0 ? errno_to_name(errno) : "-");
+                wrong += fd < 0;
+
+                fd2 = open(s, O_CLOEXEC|O_WRONLY|O_NOCTTY);
+                log_debug("open(%s, \"w\") = %d/%s", s, fd2, fd2 < 0 ? errno_to_name(errno) : "-");
+                wrong += fd2 >= 0;
+        }
+
+        {
+                _cleanup_close_ int fd, fd2;
+                const char *s = "/dev/zero";
+
+                fd = open(s, O_CLOEXEC|O_RDONLY|O_NOCTTY);
+                log_debug("open(%s, \"r\") = %d/%s", s, fd, fd < 0 ? errno_to_name(errno) : "-");
+                wrong += fd >= 0;
+
+                fd2 = open(s, O_CLOEXEC|O_WRONLY|O_NOCTTY);
+                log_debug("open(%s, \"w\") = %d/%s", s, fd2, fd2 < 0 ? errno_to_name(errno) : "-");
+                wrong += fd2 < 0;
+        }
+
+        {
+                _cleanup_close_ int fd, fd2;
+                const char *s = "/dev/full";
+
+                fd = open(s, O_CLOEXEC|O_RDONLY|O_NOCTTY);
+                log_debug("open(%s, \"r\") = %d/%s", s, fd, fd < 0 ? errno_to_name(errno) : "-");
+                wrong += fd >= 0;
+
+                fd2 = open(s, O_CLOEXEC|O_WRONLY|O_NOCTTY);
+                log_debug("open(%s, \"w\") = %d/%s", s, fd2, fd2 < 0 ? errno_to_name(errno) : "-");
+                wrong += fd2 >= 0;
+        }
+
+        assert_se(wrong == 0);
+}
+
+static void test_policy_whitelist_major(const char *pattern, const char *cgroup_path, BPFProgram **installed_prog) {
+        _cleanup_(bpf_program_unrefp) BPFProgram *prog = NULL;
+        unsigned wrong = 0;
+        int r;
+
+        log_info("/* %s(%s) */", __func__, pattern);
+
+        r = bpf_devices_cgroup_init(&prog, CGROUP_DEVICE_POLICY_STRICT, true);
+        assert_se(r >= 0);
+
+        r = bpf_devices_whitelist_major(prog, cgroup_path, pattern, 'c', "rw");
+        assert_se(r >= 0);
+
+        r = bpf_devices_apply_policy(prog, CGROUP_DEVICE_POLICY_STRICT, true, cgroup_path, installed_prog);
+        assert_se(r >= 0);
+
+        /* /dev/null, /dev/full have major==1, /dev/tty has major==5 */
+        {
+                _cleanup_close_ int fd, fd2;
+                const char *s = "/dev/null";
+
+                fd = open(s, O_CLOEXEC|O_RDONLY|O_NOCTTY);
+                log_debug("open(%s, \"r\") = %d/%s", s, fd, fd < 0 ? errno_to_name(errno) : "-");
+                wrong += fd < 0;
+
+                fd2 = open(s, O_CLOEXEC|O_WRONLY|O_NOCTTY);
+                log_debug("open(%s, \"w\") = %d/%s", s, fd2, fd2 < 0 ? errno_to_name(errno) : "-");
+                wrong += fd2 < 0;
+        }
+
+        {
+                _cleanup_close_ int fd, fd2;
+                const char *s = "/dev/full";
+
+                fd = open(s, O_CLOEXEC|O_RDONLY|O_NOCTTY);
+                log_debug("open(%s, \"r\") = %d/%s", s, fd, fd < 0 ? errno_to_name(errno) : "-");
+                wrong += fd < 0;
+
+                fd2 = open(s, O_CLOEXEC|O_WRONLY|O_NOCTTY);
+                log_debug("open(%s, \"w\") = %d/%s", s, fd2, fd2 < 0 ? errno_to_name(errno) : "-");
+                wrong += fd2 < 0;
+        }
+
+        {
+                _cleanup_close_ int fd, fd2;
+                const char *s = "/dev/tty";
+
+                fd = open(s, O_CLOEXEC|O_RDONLY|O_NOCTTY);
+                log_debug("open(%s, \"r\") = %d/%s", s, fd, fd < 0 ? errno_to_name(errno) : "-");
+                wrong += fd >= 0;
+
+                fd2 = open(s, O_CLOEXEC|O_WRONLY|O_NOCTTY);
+                log_debug("open(%s, \"w\") = %d/%s", s, fd2, fd2 < 0 ? errno_to_name(errno) : "-");
+                wrong += fd2 >= 0;
+        }
+
+        assert_se(wrong == 0);
+}
+
+static void test_policy_whitelist_major_star(char type, const char *cgroup_path, BPFProgram **installed_prog) {
+        _cleanup_(bpf_program_unrefp) BPFProgram *prog = NULL;
+        unsigned wrong = 0;
+        int r;
+
+        log_info("/* %s(type=%c) */", __func__, type);
+
+        r = bpf_devices_cgroup_init(&prog, CGROUP_DEVICE_POLICY_STRICT, true);
+        assert_se(r >= 0);
+
+        r = bpf_devices_whitelist_major(prog, cgroup_path, "*", type, "rw");
+        assert_se(r >= 0);
+
+        r = bpf_devices_apply_policy(prog, CGROUP_DEVICE_POLICY_STRICT, true, cgroup_path, installed_prog);
+        assert_se(r >= 0);
+
+        {
+                _cleanup_close_ int fd;
+                const char *s = "/dev/null";
+
+                fd = open(s, O_CLOEXEC|O_RDWR|O_NOCTTY);
+                log_debug("open(%s, \"r\") = %d/%s", s, fd, fd < 0 ? errno_to_name(errno) : "-");
+                if (type == 'c')
+                        wrong += fd < 0;
+                else
+                        wrong += fd >= 0;
+        }
+
+        assert_se(wrong == 0);
+}
+
+int main(int argc, char *argv[]) {
+        _cleanup_free_ char *cgroup = NULL, *parent = NULL;
+        _cleanup_(rmdir_and_freep) char *controller_path = NULL;
+        CGroupMask supported;
+        struct rlimit rl;
+        int r;
+
+        test_setup_logging(LOG_DEBUG);
+
+        assert_se(getrlimit(RLIMIT_MEMLOCK, &rl) >= 0);
+        rl.rlim_cur = rl.rlim_max = MAX(rl.rlim_max, CAN_MEMLOCK_SIZE);
+        (void) setrlimit(RLIMIT_MEMLOCK, &rl);
+
+        if (!can_memlock())
+                return log_tests_skipped("Can't use mlock()");
+
+        r = enter_cgroup_subroot(&cgroup);
+        if (r == -ENOMEDIUM)
+                return log_tests_skipped("cgroupfs not available");
+
+        r = bpf_devices_supported();
+        if (!r)
+                return log_tests_skipped("BPF device filter not supported");
+        assert_se(r == 1);
+
+        r = cg_get_path(SYSTEMD_CGROUP_CONTROLLER, cgroup, NULL, &controller_path);
+        assert_se(r >= 0);
+
+        _cleanup_(bpf_program_unrefp) BPFProgram *prog = NULL;
+
+        test_policy_closed(cgroup, &prog);
+        test_policy_strict(cgroup, &prog);
+
+        test_policy_whitelist_major("mem", cgroup, &prog);
+        test_policy_whitelist_major("1", cgroup, &prog);
+
+        test_policy_whitelist_major_star('c', cgroup, &prog);
+        test_policy_whitelist_major_star('b', cgroup, &prog);
+
+        assert_se(parent = dirname_malloc(cgroup));
+
+        assert_se(cg_mask_supported(&supported) >= 0);
+        r = cg_attach_everywhere(supported, parent, 0, NULL, NULL);
+        assert_se(r >= 0);
+
+        return 0;
+}