exec/file.py: add new module to write to files as root via cmd.run_root_cmd()

exec/file.py

@@ -0,0 +1,108 @@
+import logging
+import os
+import stat
+import subprocess
+
+from typing import Optional, Union
+
+from .cmd import run_root_cmd, elevation_noop, generate_cmd_su, wrap_in_bash, shell_quote
+from utils import get_user_name, get_group_name
+
+
+def try_native_filewrite(path: str, content: Union[str, bytes], chmod: Optional[str] = None) -> Optional[Exception]:
+    "try writing with python open(), return None on success, return(!) Exception on failure"
+    bflag = 'b' if isinstance(content, bytes) else ''
+    try:
+        kwargs = {}
+        if chmod:
+            kwargs['mode'] = chmod
+        descriptor = os.open(path, **kwargs)  # type: ignore
+        with open(descriptor, 'w' + bflag) as f:
+            f.write(content)
+    except Exception as ex:
+        return ex
+    return None
+
+
+def chown(path: str, user: Optional[Union[str, int]] = None, group: Optional[Union[str, int]] = None):
+    owner = ''
+    if user is not None:
+        owner += get_user_name(user)
+    if group is not None:
+        owner += f':{get_group_name(group)}'
+    if owner:
+        result = run_root_cmd(["chown", owner, path])
+        assert isinstance(result, subprocess.CompletedProcess)
+        if result.returncode:
+            raise Exception(f"Failed to change owner of '{path}' to '{owner}'")
+
+
+def root_check_exists(path):
+    return os.path.exists(path) or run_root_cmd(['[', '-e', path, ']']).returncode == 0
+
+
+def root_check_is_dir(path):
+    return os.path.isdir(path) or run_root_cmd(['[', '-d', path, ']'])
+
+
+def write_file(
+    path: str,
+    content: Union[str, bytes],
+    lazy: bool = True,
+    mode: Optional[str] = None,
+    user: Optional[str] = None,
+    group: Optional[str] = None,
+):
+    chmod = ''
+    chown_user = get_user_name(user) if user else None
+    chown_group = get_group_name(group) if group else None
+    fstat: os.stat_result
+    exists = root_check_exists(path)
+    dirname = os.path.dirname(path)
+    if exists:
+        fstat = os.stat(path)
+    else:
+        chown_user = chown_user or get_user_name(os.getuid())
+        chown_group = chown_group or get_group_name(os.getgid())
+        dir_exists = root_check_exists(dirname)
+        if not dir_exists or not root_check_is_dir(dirname):
+            reason = "is not a directory" if dir_exists else "does not exist"
+            raise Exception(f"Error writing file {path}, parent dir {reason}")
+    if mode:
+        if not mode.isnumeric():
+            raise Exception(f"Unknown file mode '{mode}' (must be numeric): {path}")
+        if not exists or stat.filemode(int(mode, 8)) != stat.filemode(fstat.st_mode):
+            chmod = mode
+    failed = try_native_filewrite(path, content, chmod)
+    if exists or failed:
+        if failed:
+            try:
+                elevation_noop(attach_tty=True)  # avoid password prompt while writing file
+                logging.debug(f"Writing to {path} using elevated /bin/tee")
+                cmd: list[str] = generate_cmd_su(wrap_in_bash(f'tee {shell_quote(path)} >/dev/null', flatten_result=False), 'root')  # type: ignore
+                assert isinstance(cmd, list)
+                s = subprocess.Popen(
+                    cmd,
+                    text=(not isinstance(content, bytes)),
+                    stdin=subprocess.PIPE,
+                )
+                s.communicate(content)
+                s.wait(300)  # 5 minute timeout
+                if s.returncode:
+                    raise Exception(f"Write command excited non-zero: {s.returncode}")
+            except Exception as ex:
+                logging.fatal(f"Writing to file '{path}' with elevated privileges failed")
+                raise ex
+        if chmod:
+            result = run_root_cmd(["chmod", chmod, path])
+            assert isinstance(result, subprocess.CompletedProcess)
+            if result.returncode:
+                raise Exception(f"Failed to set mode of '{path}' to '{chmod}'")
+
+    chown(path, chown_user, chown_group)
+
+
+def root_write_file(*args, **kwargs):
+    kwargs['user'] = 'root'
+    kwargs['group'] = 'root'
+    return write_file(*args, **kwargs)