nassh/ssh_client: rework how we pass sftp subsystem down

Rather than re-use the -s argument to select the sftp subsystem, add a
new parameter to the plugin API so we can signal this independently of
the command line.  By itself, this isn't terribly useful (and is a bit
redundant), but in a follow up CL, it allows us to simplify the command
line parsing on the JS side significantly.

BUG=chromium:725292

Change-Id: I55d04617050a3f7c76e3ecf61138ef3fad2f711c
Reviewed-on: https://chromium-review.googlesource.com/586672
Reviewed-by: Brandon Gilmore <[email protected]>
Tested-by: Mike Frysinger <[email protected]>

nassh/doc/hack.md

@@ -253,6 +253,7 @@ The session object currently has these members:
 * array `arguments`: Extra command line options for ssh.
 * int `writeWindow`: Size of the write window.
 * str `authAgentAppID`: Extension id to use as the ssh-agent.
+* str `subsystem`: Which subsystem to launch.
 
 ## NaCl->JS API
 

nassh/js/nassh_command_instance.js

@@ -706,6 +706,9 @@ nassh.CommandInstance.prototype.connectTo = function(params) {
   argv.environment = this.environment_;
   argv.writeWindow = 8 * 1024;
 
+  if (this.isSftp)
+    argv.subsystem = 'sftp';
+
   argv.arguments = ['-C'];  // enable compression
 
   if (params.authAgentAppID) {
@@ -742,9 +745,7 @@ nassh.CommandInstance.prototype.connectTo = function(params) {
   // If this is a SFTP connection, the remote command args don't make sense,
   // and will actually cause a problem.  Since it's easy to do, just ignore
   // them here.
-  if (this.isSftp) {
-    argv.arguments.push('-s', 'sftp');
-  } else if (commandArgs) {
+  if (!this.isSftp && commandArgs) {
     argv.arguments.push(commandArgs);
   }
 

ssh_client/openssh-7.5p1.patch

@@ -19,10 +19,32 @@
   */
  int
 -main(int ac, char **av)
-+ssh_main(int ac, char **av)
++ssh_main(int ac, char **av, const char *subsystem)
  {
  	struct ssh *ssh = NULL;
  	int i, r, opt, exit_status, use_syslog, direct, config_test = 0;
+@@ -971,6 +971,21 @@
+ 	/* Initialize the command to execute on remote host. */
+ 	buffer_init(&command);
+
++	if (subsystem) {
++		/*
++		 * Hijack the codeflow now that we're done parsing the command line.
++		 * We want all the flags, but none of the command line.  Unless they
++		 * passed in -s themselves.
++		 */
++		if (!subsystem_flag) {
++			subsystem_flag = 1;
++			av = xcalloc(2, sizeof(*av));
++			av[0] = subsystem;
++			av[1] = NULL;
++			ac = 1;
++		}
++	}
++
+ 	/*
+ 	 * Save the command to execute on the remote host in a buffer. There
+ 	 * is no limit on the length of the command, except by the maximum
 --- a/umac.c
 +++ b/umac.c
 @@ -1179,7 +1179,7 @@ struct umac_ctx {
@@ -62,6 +84,10 @@
  		return SSH_ERR_SYSTEM_ERROR;
 
  	/* close on exec */
+
+daemonized() relies on funcs we don't implement (because we don't need them),
+and this func is only used in sshd.  disable it to avoid link failures.
+
 --- a/misc.c
 +++ b/misc.c
 @@ -1257,6 +1257,7 @@ bind_permitted(int port, uid_t uid)

ssh_client/src/ssh_plugin.cc

@@ -40,6 +40,7 @@ const char kEnvironmentAttr[] = "environment";
 const char kArgumentsAttr[] = "arguments";
 const char kWriteWindowAttr[] = "writeWindow";
 const char kAuthAgentAppID[] = "authAgentAppID";
+const char kSubsystemAttr[] = "subsystem";
 
 // These are JavaScript method names as C++ code sees them.
 const char kPrintLogMethodId[] = "printLog";
@@ -52,7 +53,7 @@ const char kCloseMethodId[] = "close";
 
 const size_t kDefaultWriteWindow = 64 * 1024;
 
-extern "C" int ssh_main(int ac, const char** av);
+extern "C" int ssh_main(int ac, const char** av, const char *subsystem);
 
 //------------------------------------------------------------------------------
 
@@ -247,11 +248,18 @@ void SshPluginInstance::SessionThreadImpl() {
     argv.push_back(username_hostname.c_str());
   }
 
+  std::string subsystem;
+  const char *csubsystem = NULL;
+  if (session_args_.isMember(kSubsystemAttr)) {
+    subsystem = session_args_[kSubsystemAttr].asString();
+    csubsystem = subsystem.c_str();
+  }
+
   LOG("ssh main args:\n");
   for (size_t i = 0; i < argv.size(); i++)
     LOG("  argv[%d] = %s\n", i, argv[i]);
 
-  SendExitCode(ssh_main(argv.size(), &argv[0]));
+  SendExitCode(ssh_main(argv.size(), &argv[0], csubsystem));
 }
 
 void* SshPluginInstance::SessionThread(void* arg) {