Sanitize paths during archive creation and extraction

src/borg/archive.py

@@ -32,7 +32,7 @@
 from .platform import uid2user, user2uid, gid2group, group2gid
 from .helpers import parse_timestamp, archive_ts_now
 from .helpers import OutputTimestamp, format_timedelta, format_file_size, file_status, FileSize
-from .helpers import safe_encode, make_path_safe, remove_surrogates, text_to_json, join_cmd
+from .helpers import safe_encode, make_path_safe, remove_surrogates, text_to_json, join_cmd, remove_dotdot_prefixes
 from .helpers import StableDict
 from .helpers import bin_to_hex
 from .helpers import safe_ns
@@ -853,8 +853,6 @@ def same_item(item, st):
             return
 
         dest = self.cwd
-        if item.path.startswith(("/", "../")):
-            raise Exception("Path should be relative and local")
         path = os.path.join(dest, item.path)
         # Attempt to remove existing files, ignore errors on failure
         try:
@@ -1376,8 +1374,8 @@ def __init__(
 
     @contextmanager
     def create_helper(self, path, st, status=None, hardlinkable=True):
-        safe_path = make_path_safe(path)
-        item = Item(path=safe_path)
+        sanitized_path = remove_dotdot_prefixes(path)
+        item = Item(path=sanitized_path)
         hardlinked = hardlinkable and st.st_nlink > 1
         hl_chunks = None
         update_map = False

src/borg/archiver/_common.py

@@ -9,6 +9,7 @@
 from ..cache import Cache, assert_secure
 from ..helpers import Error
 from ..helpers import SortBySpec, positive_int_validator, location_validator, Location, relative_time_marker_validator
+from ..helpers import Highlander
 from ..helpers.nanorst import rst_to_terminal
 from ..manifest import Manifest, AI_HUMAN_SORT_KEYS
 from ..patterns import PatternMatcher
@@ -246,20 +247,6 @@ def wrapper(self, args, repository, manifest, **kwargs):
     return wrapper
 
 
-class Highlander(argparse.Action):
-    """make sure some option is only given once"""
-
-    def __init__(self, *args, **kwargs):
-        self.__called = False
-        super().__init__(*args, **kwargs)
-
-    def __call__(self, parser, namespace, values, option_string=None):
-        if self.__called:
-            raise argparse.ArgumentError(self, "There can be only one.")
-        self.__called = True
-        setattr(namespace, self.dest, values)
-
-
 # You can use :ref:`xyz` in the following usage pages. However, for plain-text view,
 # e.g. through "borg ... --help", define a substitution for the reference here.
 # It will replace the entire :ref:`foo` verbatim.

src/borg/archiver/create_cmd.py

@@ -27,6 +27,7 @@
 from ..helpers import flags_root, flags_dir, flags_special_follow, flags_special
 from ..helpers import sig_int, ignore_sigint
 from ..helpers import iter_separated
+from ..helpers import MakePathSafeAction
 from ..manifest import Manifest
 from ..patterns import PatternMatcher
 from ..platform import is_win32
@@ -766,7 +767,7 @@ def build_parser_create(self, subparsers, common_parser, mid_common_parser):
             metavar="NAME",
             dest="stdin_name",
             default="stdin",
-            action=Highlander,
+            action=MakePathSafeAction,
             help="use NAME in archive for stdin data (default: %(default)r)",
         )
         subparser.add_argument(

src/borg/helpers/__init__.py

@@ -13,7 +13,7 @@
 from .errors import Error, ErrorWithTraceback, IntegrityError, DecompressionError
 from .fs import ensure_dir, join_base_dir, get_socket_filename
 from .fs import get_security_dir, get_keys_dir, get_base_dir, get_cache_dir, get_config_dir, get_runtime_dir
-from .fs import dir_is_tagged, dir_is_cachedir, make_path_safe, scandir_inorder
+from .fs import dir_is_tagged, dir_is_cachedir, remove_dotdot_prefixes, make_path_safe, scandir_inorder
 from .fs import secure_erase, safe_unlink, dash_open, os_open, os_stat, umount
 from .fs import O_, flags_root, flags_dir, flags_special_follow, flags_special, flags_base, flags_normal, flags_noatime
 from .fs import HardLinkManager
@@ -31,6 +31,7 @@
 from .parseformat import BaseFormatter, ArchiveFormatter, ItemFormatter, file_status
 from .parseformat import swidth_slice, ellipsis_truncate
 from .parseformat import BorgJsonEncoder, basic_json_data, json_print, json_dump, prepare_dump_dict
+from .parseformat import Highlander, MakePathSafeAction
 from .process import daemonize, daemonizing
 from .process import signal_handler, raising_signal_handler, sig_int, ignore_sigint, SigHup, SigTerm
 from .process import popen_with_error_handling, is_terminal, prepare_subprocess_env, create_filter_process

src/borg/helpers/fs.py

@@ -217,12 +217,66 @@ def dir_is_tagged(path, exclude_caches, exclude_if_present):
     return tag_names
 
 
-_safe_re = re.compile(r"^((\.\.)?/+)+")
+def make_path_safe(path):
+    """
+    Make path safe by making it relative and normalized.
 
+    `path` is sanitized by making it relative, removing
+    consecutive slashes (e.g. '//'), removing '.' elements,
+    and removing trailing slashes.
 
-def make_path_safe(path):
-    """Make path safe by making it relative and local"""
-    return _safe_re.sub("", path) or "."
+    For reasons of security, a ValueError is raised should
+    `path` contain any '..' elements.
+    """
+    path = path.lstrip("/")
+    if "\\" in path:  # borg always wants slashes, never backslashes.
+        raise ValueError(f"unexpected backslash(es) in path {path!r}")
+    if path.startswith("../") or "/../" in path or path.endswith("/..") or path == "..":
+        raise ValueError(f"unexpected '..' element in path {path!r}")
+    path = os.path.normpath(path)
+    return path
+
+
+_dotdot_re = re.compile(r"^(\.\./)+")
+
+
+def remove_dotdot_prefixes(path):
+    """
+    Remove '../'s at the beginning of `path`. Additionally,
+    the path is made relative.
+
+    `path` is expected to be normalized already (e.g. via `os.path.normpath()`).
+    """
+    path = path.lstrip("/")
+    path = _dotdot_re.sub("", path)
+    if path in ["", ".."]:
+        return "."
+    return path
+
+
+def assert_sanitized_path(path):
+    assert isinstance(path, str)
+    # `path` should have been sanitized earlier. Some features,
+    # like pattern matching rely on a sanitized path. As a
+    # precaution we check here again.
+    if make_path_safe(path) != path:
+        raise ValueError(f"path {path!r} is not sanitized")
+    return path
+
+
+def to_sanitized_path(path):
+    assert isinstance(path, str)
+    # Legacy versions of Borg still allowed non-sanitized paths
+    # to be stored. So, we sanitize them when reading.
+    #
+    # Borg 2 ensures paths are safe before storing them. Thus, when
+    # support for reading Borg 1 archives is dropped, this should be
+    # changed to a simple check to verify paths aren't malicious.
+    # Namely, absolute paths and paths containing '..' elements must
+    # be rejected.
+    #
+    # Also checks for '..' elements in `path` for reasons of security.
+    return make_path_safe(path)
 
 
 class HardLinkManager:

src/borg/helpers/parseformat.py

@@ -19,7 +19,7 @@
 logger = create_logger()
 
 from .errors import Error
-from .fs import get_keys_dir
+from .fs import get_keys_dir, make_path_safe
 from .msgpack import Timestamp
 from .time import OutputTimestamp, format_time, safe_timestamp
 from .. import __version__ as borg_version
@@ -840,7 +840,7 @@ class FakeArchive:
 
         from ..item import Item
 
-        fake_item = Item(mode=0, path="", user="", group="", mtime=0, uid=0, gid=0)
+        fake_item = Item(mode=0, path="foo", user="", group="", mtime=0, uid=0, gid=0)
         formatter = cls(FakeArchive, "")
         keys = []
         keys.extend(formatter.call_keys.keys())
@@ -1147,3 +1147,28 @@ def decode(d):
         return res
 
     return decode(d)
+
+
+class Highlander(argparse.Action):
+    """make sure some option is only given once"""
+
+    def __init__(self, *args, **kwargs):
+        self.__called = False
+        super().__init__(*args, **kwargs)
+
+    def __call__(self, parser, namespace, values, option_string=None):
+        if self.__called:
+            raise argparse.ArgumentError(self, "There can be only one.")
+        self.__called = True
+        setattr(namespace, self.dest, values)
+
+
+class MakePathSafeAction(Highlander):
+    def __call__(self, parser, namespace, path, option_string=None):
+        try:
+            sanitized_path = make_path_safe(path)
+        except ValueError as e:
+            raise argparse.ArgumentError(self, e)
+        if sanitized_path == ".":
+            raise argparse.ArgumentError(self, f"{path!r} is not a valid file name")
+        setattr(namespace, self.dest, sanitized_path)

src/borg/item.pyx

@@ -7,6 +7,7 @@ from cpython.bytes cimport PyBytes_AsStringAndSize
 from .constants import ITEM_KEYS, ARCHIVE_KEYS
 from .helpers import StableDict
 from .helpers import format_file_size
+from .helpers.fs import assert_sanitized_path, to_sanitized_path
 from .helpers.msgpack import timestamp_to_int, int_to_timestamp, Timestamp
 from .helpers.time import OutputTimestamp, safe_timestamp
 
@@ -262,7 +263,7 @@ cdef class Item(PropDict):
 
     # properties statically defined, so that IDEs can know their names:
 
-    path = PropDictProperty(str, 'surrogate-escaped str')
+    path = PropDictProperty(str, 'surrogate-escaped str', encode=assert_sanitized_path, decode=to_sanitized_path)
     source = PropDictProperty(str, 'surrogate-escaped str')  # legacy borg 1.x. borg 2: see .target
     target = PropDictProperty(str, 'surrogate-escaped str')
     user = PropDictProperty(str, 'surrogate-escaped str')

src/borg/testsuite/__init__.py

@@ -23,6 +23,7 @@
 from ..helpers import EXIT_SUCCESS, EXIT_WARNING, EXIT_ERROR
 from .. import platform
 
+
 # Note: this is used by borg.selftest, do not use or import py.test functionality here.
 
 from ..fuse_impl import llfuse, has_pyfuse3, has_llfuse
@@ -61,6 +62,24 @@ def same_ts_ns(ts_ns1, ts_ns2):
     return diff_ts <= diff_max
 
 
+rejected_dotdot_paths = (
+    "..",
+    "../",
+    "../etc/shadow",
+    "/..",
+    "/../",
+    "/../etc",
+    "/../etc/",
+    "etc/..",
+    "/etc/..",
+    "/etc/../etc/shadow",
+    "//etc/..",
+    "etc//..",
+    "etc/..//",
+    "foo/../bar",
+)
+
+
 @contextmanager
 def unopened_tempfile():
     with tempfile.TemporaryDirectory() as tempdir:

src/borg/testsuite/archive.py

@@ -8,6 +8,7 @@
 import pytest
 
 from . import BaseTestCase
+from . import rejected_dotdot_paths
 from ..crypto.key import PlaintextKey
 from ..archive import Archive, CacheChunkBuffer, RobustUnpacker, valid_msgpacked_dict, ITEM_KEYS, Statistics
 from ..archive import BackupOSError, backup_io, backup_io_iter, get_item_uid_gid
@@ -394,3 +395,9 @@ def test_get_item_uid_gid():
     # as there is nothing, it'll fall back to uid_default/gid_default.
     assert uid == 0
     assert gid == 16
+
+
+def test_reject_non_sanitized_item():
+    for path in rejected_dotdot_paths:
+        with pytest.raises(ValueError, match="unexpected '..' element in path"):
+            Item(path=path, user="root", group="root")

src/borg/testsuite/archiver/create_cmd.py

@@ -279,6 +279,33 @@ def test_create_no_permission_file(self):
         assert "input/file2" not in out  # it skipped file2
         assert "input/file3" in out
 
+    def test_sanitized_stdin_name(self):
+        self.cmd(f"--repo={self.repository_location}", "rcreate", RK_ENCRYPTION)
+        self.cmd(f"--repo={self.repository_location}", "create", "--stdin-name", "./a//path", "test", "-", input=b"")
+        item = json.loads(self.cmd(f"--repo={self.repository_location}", "list", "test", "--json-lines"))
+        assert item["path"] == "a/path"
+
+    def test_dotdot_stdin_name(self):
+        self.cmd(f"--repo={self.repository_location}", "rcreate", RK_ENCRYPTION)
+        output = self.cmd(
+            f"--repo={self.repository_location}",
+            "create",
+            "--stdin-name",
+            "foo/../bar",
+            "test",
+            "-",
+            input=b"",
+            exit_code=2,
+        )
+        assert output.endswith("'..' element in path 'foo/../bar'" + os.linesep)
+
+    def test_dot_stdin_name(self):
+        self.cmd(f"--repo={self.repository_location}", "rcreate", RK_ENCRYPTION)
+        output = self.cmd(
+            f"--repo={self.repository_location}", "create", "--stdin-name", "./", "test", "-", input=b"", exit_code=2
+        )
+        assert output.endswith("'./' is not a valid file name" + os.linesep)
+
     def test_create_content_from_command(self):
         self.cmd(f"--repo={self.repository_location}", "rcreate", RK_ENCRYPTION)
         input_data = "some test content"
@@ -586,7 +613,7 @@ def test_exclude_keep_tagged(self):
         )
         self._assert_test_keep_tagged()
 
-    def test_path_normalization(self):
+    def test_path_sanitation(self):
         self.cmd(f"--repo={self.repository_location}", "rcreate", RK_ENCRYPTION)
         self.create_regular_file("dir1/dir2/file", size=1024 * 80)
         with changedir("input/dir1/dir2"):
@@ -595,7 +622,7 @@ def test_path_normalization(self):
         self.assert_not_in("..", output)
         self.assert_in(" input/dir1/dir2/file", output)
 
-    def test_exclude_normalization(self):
+    def test_exclude_sanitation(self):
         self.cmd(f"--repo={self.repository_location}", "rcreate", RK_ENCRYPTION)
         self.create_regular_file("file1", size=1024 * 80)
         self.create_regular_file("file2", size=1024 * 80)

src/borg/testsuite/archiver/tar_cmds.py

@@ -129,6 +129,29 @@ def test_import_tar(self, tar_format="PAX"):
             self.cmd(f"--repo={self.repository_location}", "extract", "dst")
         self.assert_dirs_equal("input", "output/input", ignore_ns=True, ignore_xattrs=True)
 
+    def test_import_unusual_tar(self):
+        # Contains these, unusual entries:
+        # /foobar
+        # ./bar
+        # ./foo2/
+        # ./foo//bar
+        # ./
+        tar_archive = os.path.join(os.path.dirname(__file__), "unusual_paths.tar")
+
+        self.cmd(f"--repo={self.repository_location}", "rcreate", "--encryption=none")
+        self.cmd(f"--repo={self.repository_location}", "import-tar", "dst", tar_archive)
+        files = self.cmd(f"--repo={self.repository_location}", "list", "dst", "--format", "{path}{NL}").splitlines()
+        self.assert_equal(set(files), {"foobar", "bar", "foo2", "foo/bar", "."})
+
+    def test_import_tar_with_dotdot(self):
+        # Contains this file:
+        # ../../../../etc/shadow
+        tar_archive = os.path.join(os.path.dirname(__file__), "dotdot_path.tar")
+
+        self.cmd(f"--repo={self.repository_location}", "rcreate", "--encryption=none")
+        with pytest.raises(ValueError, match="unexpected '..' element in path '../../../../etc/shadow'"):
+            self.cmd(f"--repo={self.repository_location}", "import-tar", "dst", tar_archive, exit_code=2)
+
     @requires_gzip
     def test_import_tar_gz(self, tar_format="GNU"):
         if not shutil.which("gzip"):
@@ -212,3 +235,8 @@ class RemoteArchiverTestCase(RemoteArchiverTestCaseBase, ArchiverTestCase):
 @unittest.skipUnless("binary" in BORG_EXES, "no borg.exe available")
 class ArchiverTestCaseBinary(ArchiverTestCaseBinaryBase, ArchiverTestCase):
     """runs the same tests, but via the borg binary"""
+
+    @unittest.skip("does not work with binaries")
+    def test_import_tar_with_dotdot(self):
+        # the test checks for a raised exception. that can't work if the code runs in a separate process.
+        pass