refactor spec parsing, map_local candidate generation

mitmproxy/addons/maplocal.py

@@ -1,52 +1,86 @@
 import mimetypes
 import re
 import typing
-import urllib
 from pathlib import Path
+
 from werkzeug.security import safe_join
 
-from mitmproxy import ctx, exceptions, http
-from mitmproxy.addons.modifyheaders import parse_modify_spec, ModifySpec
+from mitmproxy import ctx, exceptions, flowfilter, http
+from mitmproxy.addons.modifyheaders import parse_spec
+
+
+class MapLocalSpec(typing.NamedTuple):
+    matches: flowfilter.TFilter
+    regex: str
+    local_path: Path
+
+
+def parse_map_local_spec(option: str) -> MapLocalSpec:
+    filter, regex, replacement = parse_spec(option)
+
+    try:
+        re.compile(regex)
+    except re.error as e:
+        raise ValueError(f"Invalid regular expression {regex!r} ({e})")
+
+    try:
+        path = Path(replacement).expanduser().resolve(strict=True)
+    except FileNotFoundError as e:
+        raise ValueError(f"Invalid file path: {replacement} ({e})")
+
+    return MapLocalSpec(filter, regex, path)
 
 
 def get_mime_type(file_path: str) -> str:
     mimetype = (
-        mimetypes.guess_type(file_path)[0]
-        or "application/octet-stream"
+            mimetypes.guess_type(file_path)[0]
+            or "application/octet-stream"
     )
     return mimetype
 
 
-def file_candidates(url: str, base_path: str) -> typing.List[Path]:
+def _safe_path_join(root: Path, untrusted: str) -> Path:
+    """Join a Path element with an untrusted str.
+
+    This is just a convenience wrapper for werkzeug's safe_join."""
+    untrusted_parts = Path(untrusted).parts
+    joined = safe_join(
+        root.as_posix(),
+        *untrusted_parts
+    )
+    if joined is None:
+        raise ValueError("Untrusted paths.")
+    return Path(joined)
+
+
+def file_candidates(url: str, spec: MapLocalSpec) -> typing.List[Path]:
     candidates = []
-    parsed_url = urllib.parse.urlparse(url)
-    path_components = parsed_url.path.lstrip("/").split("/")
-    filename = path_components.pop()
 
-    # todo: we may want to consider other filenames such as index.htm)
-    if not filename:
-        filename = 'index.html'
+    m = re.search(spec.regex, url)
+    assert m
+    if m.groups():
+        suffix = m.group(1)
+    else:
+        suffix = re.split(spec.regex, url, maxsplit=1)[1]
+        suffix = suffix.split("?")[0]  # remove query string
 
-    # construct all possible paths
-    while True:
-        components_with_filename = tuple(path_components + [filename])
-        candidate_path = safe_join(base_path, *components_with_filename)
-        if candidate_path:
-            candidates.append(
-                Path(candidate_path)
-            )
+    suffix = re.sub(r"[^0-9a-zA-Z-_.=(),/]", "_", suffix.strip("/"))
 
-        if not path_components:
-            break
-
-        path_components.pop()
+    if suffix:
+        try:
+            candidates.append(_safe_path_join(spec.local_path, suffix))
+            candidates.append(_safe_path_join(spec.local_path, f"{suffix}/index.html"))
+        except ValueError:
+            return []
+    else:
+        candidates.append(spec.local_path / "index.html")
 
     return candidates
 
 
 class MapLocal:
     def __init__(self):
-        self.replacements: typing.List[ModifySpec] = []
+        self.replacements: typing.List[MapLocalSpec] = []
 
     def load(self, loader):
         loader.add_option(
@@ -63,7 +97,7 @@ class MapLocal:
             self.replacements = []
             for option in ctx.options.map_local:
                 try:
-                    spec = parse_modify_spec(option, True, True)
+                    spec = parse_map_local_spec(option)
                 except ValueError as e:
                     raise exceptions.OptionsError(f"Cannot parse map_local option {option}: {e}") from e
 
@@ -74,31 +108,25 @@ class MapLocal:
             return
 
         for spec in self.replacements:
-            req = flow.request
-            url = req.pretty_url
-            base_path = Path(spec.replacement)
+            url = flow.request.pretty_url
 
-            if spec.matches(flow) and re.search(spec.subject, url.encode("utf8", "surrogateescape")):
-                replacement_path = None
-                if base_path.is_file():
-                    replacement_path = base_path
-                elif base_path.is_dir():
-                    candidates = file_candidates(url, str(base_path))
-                    for candidate in candidates:
-                        # check that path is not outside of the user-defined base_path
-                        if candidate.is_file() and base_path in candidate.parents:
-                            replacement_path = candidate
+            if spec.matches(flow) and re.search(spec.regex, url):
+
+                local_file: typing.Optional[Path] = None
+
+                if spec.local_path.is_file():
+                    local_file = spec.local_path
+                elif spec.local_path.is_dir():
+                    for candidate in file_candidates(url, spec):
+                        if candidate.is_file():
+                            local_file = candidate
                             break
 
-                if replacement_path:
-                    try:
-                        flow.response = http.HTTPResponse.make(
-                            200,
-                            replacement_path.read_bytes(),
-                            {"Content-Type": get_mime_type(str(replacement_path))}
-                        )
-                        # only set flow.response once, for the first matching rule
-                        break
-                    except IOError:
-                        ctx.log.warn(f"Could not read replacement file {replacement_path}")
-                        return
+                if local_file:
+                    flow.response = http.HTTPResponse.make(
+                        200,
+                        local_file.read_bytes(),
+                        {"Content-Type": get_mime_type(str(local_file))}
+                    )
+                    # only set flow.response once, for the first matching rule
+                    return

mitmproxy/addons/mapremote.py

@@ -1,22 +1,38 @@
 import re
 import typing
 
-from mitmproxy import ctx, exceptions, http
-from mitmproxy.addons.modifyheaders import parse_modify_spec, ModifySpec
+from mitmproxy import ctx, exceptions, flowfilter, http
+from mitmproxy.addons.modifyheaders import parse_spec
+
+
+class MapRemoteSpec(typing.NamedTuple):
+    matches: flowfilter.TFilter
+    subject: str
+    replacement: str
+
+
+def parse_map_remote_spec(option: str) -> MapRemoteSpec:
+    spec = MapRemoteSpec(*parse_spec(option))
+
+    try:
+        re.compile(spec.subject)
+    except re.error as e:
+        raise ValueError(f"Invalid regular expression {spec.subject!r} ({e})")
+
+    return spec
 
 
 class MapRemote:
     def __init__(self):
-        self.replacements: typing.List[ModifySpec] = []
+        self.replacements: typing.List[MapRemoteSpec] = []
 
     def load(self, loader):
         loader.add_option(
             "map_remote", typing.Sequence[str], [],
             """
             Map remote resources to another remote URL using a pattern of the form
-            "[/flow-filter]/url-regex/[@]replacement", where the separator can
-            be any character. The @ allows to provide a file path that is
-            used to read the replacement string.
+            "[/flow-filter]/url-regex/replacement", where the separator can
+            be any character.
             """
         )
 
@@ -25,7 +41,7 @@ class MapRemote:
             self.replacements = []
             for option in ctx.options.map_remote:
                 try:
-                    spec = parse_modify_spec(option, True, False)
+                    spec = parse_map_remote_spec(option)
                 except ValueError as e:
                     raise exceptions.OptionsError(f"Cannot parse map_remote option {option}: {e}") from e
 
@@ -36,14 +52,8 @@ class MapRemote:
             return
         for spec in self.replacements:
             if spec.matches(flow):
-                try:
-                    replacement = spec.read_replacement()
-                except IOError as e:
-                    ctx.log.warn(f"Could not read replacement file: {e}")
-                    continue
-
-                url = flow.request.pretty_url.encode("utf8", "surrogateescape")
-                new_url = re.sub(spec.subject, replacement, url)
+                url = flow.request.pretty_url
+                new_url = re.sub(spec.subject, spec.replacement, url)
                 # this is a bit messy: setting .url also updates the host header,
                 # so we really only do that if the replacement affected the URL.
                 if url != new_url:

mitmproxy/addons/modifybody.py

@@ -24,7 +24,7 @@ class ModifyBody:
             self.replacements = []
             for option in ctx.options.modify_body:
                 try:
-                    spec = parse_modify_spec(option, True, False)
+                    spec = parse_modify_spec(option, True)
                 except ValueError as e:
                     raise exceptions.OptionsError(f"Cannot parse modify_body option {option}: {e}") from e
 

mitmproxy/addons/modifyheaders.py

@@ -7,10 +7,36 @@ from mitmproxy.net.http import Headers
 from mitmproxy.utils import strutils
 
 
+def _match_all(flow) -> bool:
+    return True
+
+
+def parse_spec(option: str) -> typing.Tuple[flowfilter.TFilter, str, str]:
+    """
+    Parse strings in the following format:
+
+        [/flow-filter]/subject/replacement
+
+    """
+    sep, rem = option[0], option[1:]
+    parts = rem.split(sep, 2)
+    if len(parts) == 2:
+        subject, replacement = parts
+        return _match_all, subject, replacement
+    elif len(parts) == 3:
+        patt, subject, replacement = parts
+        flow_filter = flowfilter.parse(patt)
+        if not flow_filter:
+            raise ValueError(f"Invalid filter pattern: {patt}")
+        return flow_filter, subject, replacement
+    else:
+        raise ValueError("Invalid number of parameters (2 or 3 are expected)")
+
+
 class ModifySpec(typing.NamedTuple):
     matches: flowfilter.TFilter
     subject: bytes
-    replacement: str
+    replacement_str: str
 
     def read_replacement(self) -> bytes:
         """
@@ -20,79 +46,29 @@ class ModifySpec(typing.NamedTuple):
         Raises:
             - IOError if the file cannot be read.
         """
-        if self.replacement.startswith("@"):
-            return Path(self.replacement[1:]).expanduser().read_bytes()
+        if self.replacement_str.startswith("@"):
+            return Path(self.replacement_str[1:]).expanduser().read_bytes()
         else:
             # We could cache this at some point, but unlikely to be a problem.
-            return strutils.escaped_str_to_bytes(self.replacement)
+            return strutils.escaped_str_to_bytes(self.replacement_str)
 
 
-def _match_all(flow) -> bool:
-    return True
+def parse_modify_spec(option: str, subject_is_regex: bool) -> ModifySpec:
+    flow_filter, subject_str, replacement = parse_spec(option)
 
-
-def parse_modify_spec(option, subject_is_regex: bool, replacement_is_path: bool) -> ModifySpec:
-    """
-        The form for the modify_*, map_remote, and map_local options is as follows:
-
-            * modify_body:    [/flow-filter]/body-regex/[@]replacement
-            * modify_headers: [/flow-filter]/header-name/[@]header-value
-            * map_local:      [:flow-filter]:url-regex:path
-            * map_remote:     [:flow-filter]:url-regex:[@]replacement
-
-        The @ allows to provide a file path that is used to read the respective option.
-        The addons ModifyHeaders, ModifyBody, MapRemote, and MapLocal use ModifySpec
-        to represent a single rule.
-
-        The first character specifies the separator. Example:
-
-            :~q:foo:bar
-
-        If only two clauses are specified, the flow filter is set to
-        match universally (i.e. ".*"). Example:
-
-            /foo/bar
-
-        Clauses are parsed from left to right. Extra separators are taken to be
-        part of the final clause. For instance, the last parameter (header-value,
-        replace, or path) below is "foo/bar/":
-
-            /one/two/foo/bar/
-    """
-    sep, rem = option[0], option[1:]
-    parts = rem.split(sep, 2)
-    if len(parts) == 2:
-        flow_filter = _match_all
-        subject, replacement = parts
-    elif len(parts) == 3:
-        flow_filter_pattern, subject, replacement = parts
-        flow_filter = flowfilter.parse(flow_filter_pattern)  # type: ignore
-        if not flow_filter:
-            raise ValueError(f"Invalid filter pattern: {flow_filter_pattern}")
-    else:
-        raise ValueError("Invalid number of parameters (2 or 3 are expected)")
-
-    subject = strutils.escaped_str_to_bytes(subject)
+    subject = strutils.escaped_str_to_bytes(subject_str)
     if subject_is_regex:
         try:
             re.compile(subject)
         except re.error as e:
             raise ValueError(f"Invalid regular expression {subject!r} ({e})")
 
-    if replacement_is_path:
-        path = Path(replacement)
-        try:
-            replacement = str(path.expanduser().resolve(strict=True))
-        except FileNotFoundError as e:
-            raise ValueError(f"Invalid file path: {replacement} ({e})")
-
     spec = ModifySpec(flow_filter, subject, replacement)
 
-    if not replacement_is_path:
-        try:
-            spec.read_replacement()
-        except IOError as e:
-            raise ValueError(f"Invalid file path: {replacement[1:]} ({e})")
+    try:
+        spec.read_replacement()
+    except IOError as e:
+        raise ValueError(f"Invalid file path: {replacement[1:]} ({e})")
 
     return spec
 
@@ -116,7 +92,7 @@ class ModifyHeaders:
         if "modify_headers" in updated:
             for option in ctx.options.modify_headers:
                 try:
-                    spec = parse_modify_spec(option, False, False)
+                    spec = parse_modify_spec(option, False)
                 except ValueError as e:
                     raise exceptions.OptionsError(f"Cannot parse modify_headers option {option}: {e}") from e
                 self.replacements.append(spec)

test/mitmproxy/addons/test_maplocal.py

@@ -1,35 +1,59 @@
+import re
+from pathlib import Path
+
 import pytest
 
-from mitmproxy.addons.maplocal import MapLocal, file_candidates
+from mitmproxy.addons.maplocal import MapLocal, MapLocalSpec, file_candidates
+from mitmproxy.addons.modifyheaders import parse_spec
 from mitmproxy.test import taddons
 from mitmproxy.test import tflow
 
-from mitmproxy.addons.modifyheaders import parse_modify_spec
-
 
 @pytest.mark.parametrize(
-    "url,spec,expected_candidates", [
+    "url,spec,expected_candidates",
+    [
+        # trailing slashes
+        ("https://example.com/foo", ":example.com/foo:/tmp", ["/tmp/index.html"]),
+        ("https://example.com/foo/", ":example.com/foo:/tmp", ["/tmp/index.html"]),
+        ("https://example.com/foo", ":example.com/foo:/tmp/", ["/tmp/index.html"]),
+    ] + [
+        # simple prefixes
+        ("http://example/foo/bar.jpg", ":example/foo:/tmp", ["/tmp/bar.jpg", "/tmp/bar.jpg/index.html"]),
+        ("https://example/foo/bar.jpg", ":example/foo:/tmp", ["/tmp/bar.jpg", "/tmp/bar.jpg/index.html"]),
+        ("https://example/foo/bar.jpg?query", ":example/foo:/tmp", ["/tmp/bar.jpg", "/tmp/bar.jpg/index.html"]),
+        ("https://example/foo/bar/baz.jpg", ":example/foo:/tmp", ["/tmp/bar/baz.jpg", "/tmp/bar/baz.jpg/index.html"]),
+    ] + [
+        # index.html
+        ("https://example.com/foo", ":example.com/foo:/tmp", ["/tmp/index.html"]),
+        ("https://example.com/foo/", ":example.com/foo:/tmp", ["/tmp/index.html"]),
+        ("https://example.com/foo/bar", ":example.com/foo:/tmp", ["/tmp/bar", "/tmp/bar/index.html"]),
+        ("https://example.com/foo/bar/", ":example.com/foo:/tmp", ["/tmp/bar", "/tmp/bar/index.html"]),
+    ] + [
+        # regex
         (
-            "https://example.org/img/topic/subtopic/test.jpg",
-            ":example.com/foo:/tmp",
-            ["/tmp/img/topic/subtopic/test.jpg", "/tmp/img/topic/test.jpg", "/tmp/img/test.jpg", "/tmp/test.jpg"]
-        ),
-        (
-            "https://example.org/img/topic/subtopic/",
-            ":/img:/tmp",
-            ["/tmp/img/topic/subtopic/index.html", "/tmp/img/topic/index.html", "/tmp/img/index.html", "/tmp/index.html"]
-        ),
-        (
-            "https://example.org",
-            ":org:/tmp",
-            ["/tmp/index.html"]
+                "https://example/view.php?f=foo.jpg",
+                ":example/view.php\\?f=(.+):/tmp",
+                ["/tmp/foo.jpg", "/tmp/foo.jpg/index.html"]
+        ), (
+                "https://example/results?id=1&foo=2",
+                ":example/(results\\?id=.+):/tmp",
+                ["/tmp/results_id=1_foo=2", "/tmp/results_id=1_foo=2/index.html"]
         ),
+    ] + [
+        # test directory traversal detection
+        ("https://example.com/../../../../../../etc/passwd", ":example.com:/tmp", []),
+        # those get already sanitized to benign versions before they reach our detection:
+        ("https://example.com/C:\\foo.txt", ":example.com:/tmp", ["/tmp/C__foo.txt", "/tmp/C__foo.txt/index.html"]),
+        ("https://example.com//etc/passwd", ":example.com:/tmp", ["/tmp/etc/passwd", "/tmp/etc/passwd/index.html"]),
     ]
 )
 def test_file_candidates(url, spec, expected_candidates):
-    spec = parse_modify_spec(spec, True, True)
-    candidates = file_candidates(url, spec.replacement)
-    assert [str(x) for x in candidates] == expected_candidates
+    # we circumvent the path existence checks here to simplify testing
+    filt, subj, repl = parse_spec(spec)
+    spec = MapLocalSpec(filt, subj, Path(repl))
+
+    candidates = file_candidates(url, spec)
+    assert [x.as_posix() for x in candidates] == expected_candidates
 
 
 class TestMapLocal: