datamodel/types/files.py: improve file permission check

In particular with ACLs this could have prevented resolver starting
even if the permissions were OK.  os.access() should be accurate
at least when running from manager (not from kresctl).

diff --git a/python/knot_resolver/datamodel/types/files.py b/python/knot_resolver/datamodel/types/files.py
index 9e326999b2436bd98e1b118cd5be382b4266d87c..b19237fa2554b1487672de24bb6835cd0e6118f1 100644 (file)
--- a/python/knot_resolver/datamodel/types/files.py
+++ b/python/knot_resolver/datamodel/types/files.py
@@ -1,3 +1,4 @@
+import logging
 import os
 import stat
 from enum import Flag, auto
@@ -10,6 +11,8 @@ from knot_resolver.constants import GROUP, USER
 from knot_resolver.datamodel.globals import get_permissions_default, get_resolve_root, get_strict_validation
 from knot_resolver.utils.modeling.base_value_type import BaseValueType
 
+logger = logging.getLogger(__name__)
+
 
 class UncheckedPath(BaseValueType):
     """
@@ -157,8 +160,7 @@ class _PermissionMode(Flag):
     WRITE = auto()
     EXECUTE = auto()
 
-
-def _kres_accessible(dest_path: Path, perm_mode: _PermissionMode) -> bool:
+def _check_permission(dest_path: Path, perm_mode: _PermissionMode) -> bool:
     chflags = {
         _PermissionMode.READ: [stat.S_IRUSR, stat.S_IRGRP, stat.S_IROTH],
         _PermissionMode.WRITE: [stat.S_IWUSR, stat.S_IWGRP, stat.S_IWOTH],
@@ -208,8 +210,11 @@ class ReadableFile(File):
     ) -> None:
         super().__init__(source_value, parents=parents, object_path=object_path)
 
-        if self.strict_validation and not _kres_accessible(self._value, _PermissionMode.READ):
-            raise ValueError(f"{USER}:{GROUP} has insufficient permissions to read '{self._value}'")
+        if self.strict_validation and not _check_permission(self._value, _PermissionMode.READ):
+            msg = f"{USER}:{GROUP} has insufficient permissions to read '{self._value}'"
+            if not os.access(self._value, os.R_OK):
+                raise ValueError(msg)
+            logger.info(f"{msg}, but the resolver can somehow (ACLs, ...) read the file")
 
 
 class WritableDir(Dir):
@@ -224,10 +229,13 @@ class WritableDir(Dir):
     ) -> None:
         super().__init__(source_value, parents=parents, object_path=object_path)
 
-        if self.strict_validation and not _kres_accessible(
+        if self.strict_validation and not _check_permission(
             self._value, _PermissionMode.WRITE | _PermissionMode.EXECUTE
         ):
-            raise ValueError(f"{USER}:{GROUP} has insufficient permissions to write/execute '{self._value}'")
+            msg = f"{USER}:{GROUP} has insufficient permissions to write/execute '{self._value}'"
+            if not os.access(self._value, os.W_OK | os.X_OK):
+                raise ValueError(msg)
+            logger.info(f"{msg}, but the resolver can somehow (ACLs, ...) write to the directory")
 
 
 class WritableFilePath(FilePath):
@@ -243,7 +251,21 @@ class WritableFilePath(FilePath):
     ) -> None:
         super().__init__(source_value, parents=parents, object_path=object_path)
 
-        if self.strict_validation and not _kres_accessible(
-            self._value.parent, _PermissionMode.WRITE | _PermissionMode.EXECUTE
-        ):
-            raise ValueError(f"{USER}:{GROUP} has insufficient permissions to write/execute'{self._value.parent}'")
+        if self.strict_validation:
+            # check that parent dir is writable
+            if not _check_permission(self._value.parent, _PermissionMode.WRITE | _PermissionMode.EXECUTE):
+                msg = f"{USER}:{GROUP} has insufficient permissions to write/execute '{self._value.parent}'"
+                # os.access() on the dir just provides a more precise message,
+                # as the os.access() on the file below check everything in one go
+                if not os.access(self._value.parent, os.W_OK | os.X_OK):
+                    raise ValueError(msg)
+                logger.info(f"{msg}, but the resolver can somehow (ACLs, ...) write to the directory")
+
+            # check that existing file is writable
+            if self._value.exists() and not _check_permission(
+                self._value, _PermissionMode.WRITE
+            ):
+                msg = f"{USER}:{GROUP} has insufficient permissions to write/execute '{self._value}'"
+                if not os.access(self._value, os.W_OK):
+                    raise ValueError(msg)
+                logger.info(f"{msg}, but the resolver can somehow (ACLs, ...) write to the file")