Add timeout for mount on untrusted media

Under some circumstances it seems mounting a device can take a long
time. We already abort fsck if it runs for too long, so this is the last
remaining spot this could happen.

Bug: 339740354
Test: Mount a very slow device, observe no Android restart
Change-Id: I3607be269d3aeb4c2391d1d8e2372e3a6795e7c4
diff --git a/Utils.cpp b/Utils.cpp
index a3db43e..c4070d1 100644
--- a/Utils.cpp
+++ b/Utils.cpp
@@ -754,6 +754,57 @@
     return OK;
 }
 
+status_t ForkTimeout(int (*func)(void*), void* args, std::chrono::seconds timeout) {
+    int status;
+
+    // We're waiting on either the timeout or workload process to finish, so we're
+    // initially forking to get away from any other vold children
+    pid_t wait_timeout_pid = fork();
+    if (wait_timeout_pid == 0) {
+        pid_t pid = fork();
+        if (pid == 0) {
+            _exit(func(args));
+        }
+        if (pid == -1) {
+            _exit(EXIT_FAILURE);
+        }
+        pid_t timer_pid = fork();
+        if (timer_pid == 0) {
+            std::this_thread::sleep_for(timeout);
+            _exit(ETIMEDOUT);
+        }
+        if (timer_pid == -1) {
+            PLOG(ERROR) << "fork in ForkTimeout failed";
+            kill(pid, SIGTERM);
+            _exit(EXIT_FAILURE);
+        }
+        // Preserve the exit code of the first process to finish, and end the other
+        pid_t finished = wait(&status);
+        if (finished == pid) {
+            kill(timer_pid, SIGTERM);
+        } else {
+            kill(pid, SIGTERM);
+        }
+        if (!WIFEXITED(status)) {
+            _exit(ECHILD);
+        }
+        _exit(WEXITSTATUS(status));
+    }
+    if (waitpid(wait_timeout_pid, &status, 0) == -1) {
+        PLOG(ERROR) << "waitpid in ForkTimeout failed";
+        return -errno;
+    }
+    if (!WIFEXITED(status)) {
+        LOG(ERROR) << "Process did not exit normally, status: " << status;
+        return -ECHILD;
+    }
+    if (WEXITSTATUS(status)) {
+        LOG(ERROR) << "Process exited with code: " << WEXITSTATUS(status);
+        return WEXITSTATUS(status);
+    }
+    return OK;
+}
+
 status_t ForkExecvpTimeout(const std::vector<std::string>& args, std::chrono::seconds timeout,
                            char* context) {
     int status;