SSHDriver: implement user switching via su

doc/configuration.rst

@@ -1573,6 +1573,13 @@ Arguments:
     target.
   - explicit_sftp_mode (bool, default=False): if set to True, `put()` and `get()` will
     explicitly use the SFTP protocol for file transfers instead of scp's default protocol
+  - su_username(str, default="root"): only used if su_password is set
+  - su_prompt(str, default="Password:"): prompt string for su
+  - su_password(str): optional, su password for the user set via su_username
+
+.. note::
+   Using the su support will automatically enable ``stderr_merge``, since this
+   is required to interact with the password prompt.
 
 UBootDriver
 ~~~~~~~~~~~

examples/ssh-su-example/conf.yaml

@@ -0,0 +1,11 @@
+targets:
+  main:
+    resources:
+      NetworkService:
+        address: 127.0.0.1
+        username: <login_username>
+    drivers:
+      SSHDriver:
+        su_password: <the_password>
+        su_username: <the_username>
+        stderr_merge: true

examples/ssh-su-example/test.py

@@ -0,0 +1,14 @@
+import logging
+
+from labgrid import Environment
+
+logging.basicConfig(
+        level=logging.DEBUG
+)
+
+env = Environment("conf.yaml")
+target = env.get_target()
+ssh = target.get_driver("SSHDriver")
+out, _, code = ssh.run("ps -p $PPID")
+print(code)
+print(out)

labgrid/driver/sshdriver.py

@@ -11,6 +11,8 @@
 import time
 
 import attr
+from pexpect.fdpexpect import fdspawn
+from pexpect.exceptions import EOF, TIMEOUT
 
 from ..factory import target_factory
 from ..protocol import CommandProtocol, FileTransferProtocol
@@ -22,6 +24,7 @@
 from ..util.proxy import proxymanager
 from ..util.timeout import Timeout
 from ..util.ssh import get_ssh_connect_timeout
+from ..util.marker import gen_marker
 
 
 @target_factory.reg_driver
@@ -34,6 +37,9 @@ class SSHDriver(CommandMixin, Driver, CommandProtocol, FileTransferProtocol):
     stderr_merge = attr.ib(default=False, validator=attr.validators.instance_of(bool))
     connection_timeout = attr.ib(default=float(get_ssh_connect_timeout()), validator=attr.validators.instance_of(float))
     explicit_sftp_mode = attr.ib(default=False, validator=attr.validators.instance_of(bool))
+    su_password = attr.ib(default=None, validator=attr.validators.optional(attr.validators.instance_of(str)))
+    su_username = attr.ib(default="root", validator=attr.validators.instance_of(str))
+    su_prompt = attr.ib(default="Password:", validator=attr.validators.instance_of(str))
 
     def __attrs_post_init__(self):
         super().__attrs_post_init__()
@@ -180,6 +186,40 @@ def _start_own_master_once(self, timeout):
     def run(self, cmd, codec="utf-8", decodeerrors="strict", timeout=None):
         return self._run(cmd, codec=codec, decodeerrors=decodeerrors, timeout=timeout)
 
+    def handle_password(self, fd, stdin, marker):
+        p = fdspawn(fd, timeout=15)
+        try:
+            p.expect([f"{marker}\n"])
+        except TIMEOUT:
+            raise ExecutionError(f"Failed to find marker before su: {p.buffer!r}")
+        except EOF:
+            raise ExecutionError("Unexpected disconnect before su")
+
+        try:
+            index = p.expect([f"{marker}\n", self.su_prompt])
+        except TIMEOUT:
+            raise ExecutionError(f"Unexpected output from su: {p.buffer!r}")
+        except EOF:
+            raise ExecutionError("Unexpected disconnect after starting su")
+
+        if index == 0:
+            # no password needed
+            return p.after
+
+        stdin.write(self.su_password.encode("utf-8"))
+        # It seems we need to close stdin here to reliably get su to accept the
+        # password. \n doesn't seem to work.
+        stdin.close()
+
+        try:
+            p.expect([f"{marker}\n"])
+        except TIMEOUT:
+            raise ExecutionError(f"Unexpected output from su after entering password: {p.buffer!r}")
+        except EOF:
+            raise ExecutionError(f"Unexpected disconnect after after entering su password: {p.before!r}")
+
+        return p.after
+
     def _run(self, cmd, codec="utf-8", decodeerrors="strict", timeout=None):
         """Execute `cmd` on the target.
 
@@ -193,25 +233,47 @@ def _run(self, cmd, codec="utf-8", decodeerrors="strict", timeout=None):
         if not self._check_keepalive():
             raise ExecutionError("Keepalive no longer running")
 
-        complete_cmd = ["ssh", "-x", *self.ssh_prefix,
+        complete_cmd = ["ssh", "-x", "-o", "LogLevel=QUIET", *self.ssh_prefix,
                         "-p", str(self.networkservice.port), "-l", self.networkservice.username,
                         self.networkservice.address
-                        ] + cmd.split(" ")
+                        ]
+        if self.su_password:
+            self.stderr_merge = True  # with -tt, we get all output on stdout
+            marker = gen_marker()
+            complete_cmd += ["-tt", "--", "echo", f"{marker};", "su", self.su_username, "--"]
+            inner_cmd = f"echo '{marker[:4]}''{marker[4:]}'; {cmd}"
+            complete_cmd += ["-c", shlex.quote(inner_cmd)]
+        else:
+            complete_cmd += ["--"] + cmd.split(" ")
+
         self.logger.debug("Sending command: %s", complete_cmd)
         if self.stderr_merge:
             stderr_pipe = subprocess.STDOUT
         else:
             stderr_pipe = subprocess.PIPE
+        stdin = subprocess.PIPE if self.su_password else None
+        stdout, stderr = b"", b""
         try:
             sub = subprocess.Popen(
-                complete_cmd, stdout=subprocess.PIPE, stderr=stderr_pipe
+                complete_cmd, stdout=subprocess.PIPE, stderr=stderr_pipe, stdin=stdin,
             )
         except:
             raise ExecutionError(
                 f"error executing command: {complete_cmd}"
             )
 
-        stdout, stderr = sub.communicate(timeout=timeout)
+        if self.su_password:
+            output = self.handle_password(sub.stdout, sub.stdin, marker)
+            sub.stdin.close()
+            self.logger.debug("su leftover output: %s", output)
+            stderr += output
+            sub.stdin = None  # never try to write to stdin here
+
+        comout, comerr = sub.communicate(timeout=timeout)
+        stdout += comout
+        if not self.stderr_merge:
+            stderr += comerr
+
         stdout = stdout.decode(codec, decodeerrors).split('\n')
         if stdout[-1] == '':
             stdout.pop()