tests: add a fuzzer for the udev rules parser (#10929)

src/fuzz/fuzz-main.c

@@ -36,7 +36,8 @@ int main(int argc, char **argv) {
                 printf("%s... ", name);
                 fflush(stdout);
                 for (int j = 0; j < MIN_NUMBER_OF_RUNS; j++)
-                        (void) LLVMFuzzerTestOneInput((uint8_t*)buf, size);
+                        if (LLVMFuzzerTestOneInput((uint8_t*)buf, size) == EXIT_TEST_SKIP)
+                                return EXIT_TEST_SKIP;
                 printf("ok\n");
         }
 

src/fuzz/fuzz-udev-rules.c

@@ -0,0 +1,95 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+
+#include <errno.h>
+#include <sched.h>
+#include <sys/mount.h>
+#include <unistd.h>
+
+#include "fd-util.h"
+#include "fs-util.h"
+#include "fuzz.h"
+#include "log.h"
+#include "mkdir.h"
+#include "missing.h"
+#include "rm-rf.h"
+#include "string-util.h"
+#include "tests.h"
+#include "udev.h"
+
+static const struct fakefs {
+        const char *target;
+        bool ignore_mount_error;
+} fakefss[] = {
+        { "/sys",                    false },
+        { "/dev",                    false },
+        { "/run",                    false },
+        { "/etc",                    false },
+        { UDEVLIBEXECDIR "/rules.d", true },
+};
+
+static int setup_mount_namespace(void) {
+        static thread_local bool is_namespaced = false;
+
+        if (is_namespaced)
+                return 1;
+
+        if (unshare(CLONE_NEWNS) < 0)
+                return log_error_errno(errno, "Failed to call unshare(): %m");
+
+        if (mount(NULL, "/", NULL, MS_SLAVE|MS_REC, NULL) < 0)
+                return log_error_errno(errno, "Failed to mount / as private: %m");
+
+        is_namespaced = true;
+
+        return 1;
+}
+
+static int setup_fake_filesystems(const char *runtime_dir) {
+        for (unsigned i = 0; i < ELEMENTSOF(fakefss); i++)
+                if (mount(runtime_dir, fakefss[i].target, NULL, MS_BIND, NULL) < 0) {
+                        log_full_errno(fakefss[i].ignore_mount_error ? LOG_DEBUG : LOG_ERR, errno, "Failed to mount %s: %m", fakefss[i].target);
+                        if (!fakefss[i].ignore_mount_error)
+                                return -errno;
+                }
+
+        return 0;
+}
+
+static int cleanup_fake_filesystems(const char *runtime_dir) {
+        for (unsigned i = 0; i < ELEMENTSOF(fakefss); i++)
+                if (umount(fakefss[i].target) < 0) {
+                        log_full_errno(fakefss[i].ignore_mount_error ? LOG_DEBUG : LOG_ERR, errno, "Failed to umount %s: %m", fakefss[i].target);
+                        if (!fakefss[i].ignore_mount_error)
+                                return -errno;
+                }
+        return 0;
+}
+
+int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
+        _cleanup_(udev_rules_freep) struct udev_rules *rules = NULL;
+        _cleanup_(rm_rf_physical_and_freep) char *runtime_dir = NULL;
+        FILE *f = NULL;
+
+        if (!getenv("SYSTEMD_LOG_LEVEL")) {
+                log_set_max_level_realm(LOG_REALM_UDEV, LOG_CRIT);
+                log_set_max_level_realm(LOG_REALM_SYSTEMD, LOG_CRIT);
+        }
+
+        if (setup_mount_namespace() < 0)
+                return EXIT_TEST_SKIP;
+
+        assert_se(runtime_dir = setup_fake_runtime_dir());
+
+        assert_se(setup_fake_filesystems(runtime_dir) >= 0);
+        assert_se(mkdir_p("/etc/udev/rules.d", 0755) >= 0);
+        f = fopen("/etc/udev/rules.d/fuzz.rules", "we");
+        assert_se(f);
+        if (size != 0)
+                assert_se(fwrite(data, size, 1, f) == 1);
+        assert_se(fclose(f) == 0);
+        rules = udev_rules_new(RESOLVE_NAME_EARLY);
+
+        assert_se(cleanup_fake_filesystems(runtime_dir) >= 0);
+
+        return 0;
+}

src/fuzz/meson.build

@@ -97,6 +97,14 @@ fuzzers += [
           libshared],
          []],
 
+        [['src/fuzz/fuzz-udev-rules.c'],
+         [libudev_core,
+          libudev_static,
+          libsystemd_network,
+          libshared],
+         [threads,
+          libacl]],
+
         [['src/fuzz/fuzz-compress.c'],
          [libshared],
          []],