fuzz-udev-rules: rewrite to not require root privileges

Fixes https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=20142.

It turns out we don't need to do all this preparatory work if we want to parse
just one file.

1 files changed, 8 insertions, 83 deletions

diff --git a/src/fuzz/fuzz-udev-rules.c b/src/fuzz/fuzz-udev-rules.c
index a4a1adec3e..dd3c403ebb 100644
--- a/src/fuzz/fuzz-udev-rules.c
+++ b/src/fuzz/fuzz-udev-rules.c
@@ -1,106 +1,31 @@
 /* SPDX-License-Identifier: LGPL-2.1+ */
 
-#include <errno.h>
-#include <sched.h>
-#include <sys/mount.h>
-#include <unistd.h>
+#include <stdio.h>
 
 #include "fd-util.h"
 #include "fs-util.h"
 #include "fuzz.h"
-#include "log.h"
-#include "mkdir.h"
-#include "rm-rf.h"
-#include "string-util.h"
 #include "tests.h"
+#include "tmpfile-util.h"
 #include "udev-rules.h"
 
-static struct fakefs {
-        const char *target;
-        bool ignore_mount_error;
-        bool is_mounted;
-} fakefss[] = {
-        { "/sys",                    false, false },
-        { "/dev",                    false, false },
-        { "/run",                    false, false },
-        { "/etc",                    false, false },
-        { UDEVLIBEXECDIR "/rules.d", true, false },
-};
-
-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;
-                } else
-                        fakefss[i].is_mounted = true;
-        }
-
-        return 0;
-}
-
-static int cleanup_fake_filesystems(const char *runtime_dir) {
-        for (unsigned i = 0; i < ELEMENTSOF(fakefss); i++) {
-                if (!fakefss[i].is_mounted)
-                        continue;
-
-                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;
-                } else
-                        fakefss[i].is_mounted = false;
-        }
-        return 0;
-}
-
 int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
         _cleanup_(udev_rules_freep) UdevRules *rules = NULL;
-        _cleanup_(rm_rf_physical_and_freep) char *runtime_dir = NULL;
-        FILE *f = NULL;
-
-        (void) setup_mount_namespace();
-
-        assert_se(runtime_dir = setup_fake_runtime_dir());
-
-        if (setup_fake_filesystems(runtime_dir) < 0) {
-#ifndef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
-                return EXIT_TEST_SKIP;
-#endif
-        }
+        _cleanup_fclose_ FILE *f = NULL;
+        _cleanup_(unlink_tempfilep) char filename[] = "/tmp/fuzz-udev-rules.XXXXXX";
 
         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);
         }
 
-        assert_se(mkdir_p("/etc/udev/rules.d", 0755) >= 0);
-        f = fopen("/etc/udev/rules.d/fuzz.rules", "we");
-        assert_se(f);
+        assert_se(fmkostemp_safe(filename, "r+", &f) == 0);
         if (size != 0)
                 assert_se(fwrite(data, size, 1, f) == 1);
-        assert_se(fclose(f) == 0);
+        fflush(f);
 
-        assert_se(udev_rules_load(&rules, RESOLVE_NAME_EARLY) == 0);
+        assert_se(rules = udev_rules_new(RESOLVE_NAME_EARLY));
+        assert_se(udev_rules_parse_file(rules, filename) == 0);
 
-        assert_se(cleanup_fake_filesystems(runtime_dir) >= 0);
         return 0;
 }