adb: fix fd double close, Subprocess lifetime issue.

This commit fixes two somewhat related issues in shell_service.

  - The fd returned by StartSubprocess is owned by a unique_fd
    contained in the Subprocess object, but also gets closed by the
    caller. Resolve this by duping the returned file descriptor.

  - A Subprocess object can be destroyed immediately after its initial
    construction in StartSubprocess if we're sufficiently unlucky.
    Split up the fork/exec and "start management thread" steps, so that
    we can safely do everything we need to do on the Subprocess before
    handing it over to the thread that'll eventually destroy it.

Bug: http://b/29254462
Change-Id: Id9cf0b7e7a7293bee7176919edc758597691c636

adb/shell_service.cpp

@@ -160,9 +160,14 @@ class Subprocess {
     pid_t pid() const { return pid_; }
 
     // Sets up FDs, forks a subprocess, starts the subprocess manager thread,
-    // and exec's the child. Returns false on failure.
+    // and exec's the child. Returns false and sets error on failure.
     bool ForkAndExec(std::string* _Nonnull error);
 
+    // Start the subprocess manager thread. Consumes the subprocess, regardless of success.
+    // Returns false and sets error on failure.
+    static bool StartThread(std::unique_ptr<Subprocess> subprocess,
+                            std::string* _Nonnull error);
+
   private:
     // Opens the file at |pts_name|.
     int OpenPtyChildFd(const char* pts_name, unique_fd* error_sfd);
@@ -390,14 +395,19 @@ bool Subprocess::ForkAndExec(std::string* error) {
         }
     }
 
-    if (!adb_thread_create(ThreadHandler, this)) {
+    D("subprocess parent: completed");
+    return true;
+}
+
+bool Subprocess::StartThread(std::unique_ptr<Subprocess> subprocess, std::string* error) {
+    Subprocess* raw = subprocess.release();
+    if (!adb_thread_create(ThreadHandler, raw)) {
         *error =
             android::base::StringPrintf("failed to create subprocess thread: %s", strerror(errno));
-        kill(pid_, SIGKILL);
+        kill(raw->pid_, SIGKILL);
         return false;
     }
 
-    D("subprocess parent: completed");
     return true;
 }
 
@@ -441,6 +451,7 @@ void Subprocess::ThreadHandler(void* userdata) {
     adb_thread_setname(android::base::StringPrintf(
             "shell srvc %d", subprocess->local_socket_fd()));
 
+    D("passing data streams for PID %d", subprocess->pid());
     subprocess->PassDataStreams();
 
     D("deleting Subprocess for PID %d", subprocess->pid());
@@ -733,7 +744,7 @@ int StartSubprocess(const char* name, const char* terminal_type,
       protocol == SubprocessProtocol::kNone ? "none" : "shell",
       terminal_type, name);
 
-    Subprocess* subprocess = new Subprocess(name, terminal_type, type, protocol);
+    auto subprocess = std::make_unique<Subprocess>(name, terminal_type, type, protocol);
     if (!subprocess) {
         LOG(ERROR) << "failed to allocate new subprocess";
         return ReportError(protocol, "failed to allocate new subprocess");
@@ -742,11 +753,17 @@ int StartSubprocess(const char* name, const char* terminal_type,
     std::string error;
     if (!subprocess->ForkAndExec(&error)) {
         LOG(ERROR) << "failed to start subprocess: " << error;
-        delete subprocess;
         return ReportError(protocol, error);
     }
 
-    D("subprocess creation successful: local_socket_fd=%d, pid=%d",
-      subprocess->local_socket_fd(), subprocess->pid());
-    return subprocess->local_socket_fd();
+    unique_fd local_socket(dup(subprocess->local_socket_fd()));
+    D("subprocess creation successful: local_socket_fd=%d, pid=%d", local_socket.get(),
+      subprocess->pid());
+
+    if (!Subprocess::StartThread(std::move(subprocess), &error)) {
+        LOG(ERROR) << "failed to start subprocess management thread: " << error;
+        return ReportError(protocol, error);
+    }
+
+    return local_socket.release();
 }