gh-139633: Run netrc file permission check only once per parse

Change the `.netrc` security check to be run once per parse of the
default file rather than once per line inside the file.

Author: cmaloney

Lib/netrc.py

@@ -152,23 +152,28 @@ def _parse(self, file, fp, default_netrc):
                 else:
                     raise NetrcParseError("bad follower token %r" % tt,
                                           file, lexer.lineno)
-            self._security_check(fp, default_netrc, self.hosts[entryname][0])
-
-    def _security_check(self, fp, default_netrc, login):
-        if _can_security_check() and default_netrc and login != "anonymous":
-            prop = os.fstat(fp.fileno())
-            current_user_id = os.getuid()
-            if prop.st_uid != current_user_id:
-                fowner = _getpwuid(prop.st_uid)
-                user = _getpwuid(current_user_id)
-                raise NetrcParseError(
-                    f"~/.netrc file owner ({fowner}) does not match"
-                    f" current user ({user})")
-            if (prop.st_mode & (stat.S_IRWXG | stat.S_IRWXO)):
-                raise NetrcParseError(
-                    "~/.netrc access too permissive: access"
-                    " permissions must restrict access to only"
-                    " the owner")
+
+        if _can_security_check() and default_netrc:
+            for entry in self.hosts.values():
+                if entry[0] != "anonymous":
+                    # Raises on security issue
+                    self._security_check(fp)
+                    break
+
+    def _security_check(self, fp):
+        prop = os.fstat(fp.fileno())
+        current_user_id = os.getuid()
+        if prop.st_uid != current_user_id:
+            fowner = _getpwuid(prop.st_uid)
+            user = _getpwuid(current_user_id)
+            raise NetrcParseError(
+                f"~/.netrc file owner ({fowner}) does not match"
+                f" current user ({user})")
+        if (prop.st_mode & (stat.S_IRWXG | stat.S_IRWXO)):
+            raise NetrcParseError(
+                "~/.netrc access too permissive: access"
+                " permissions must restrict access to only"
+                " the owner")
 
     def authenticators(self, host):
         """Return a (user, account, password) tuple for given host."""

Lib/test/test_netrc.py

@@ -1,6 +1,9 @@
 import netrc, os, unittest, sys, textwrap
+from pathlib import Path
 from test import support
 from test.support import os_helper
+from unittest.mock import Mock
+
 
 temp_filename = os_helper.TESTFN
 
@@ -309,6 +312,29 @@ def test_security(self):
             self.assertEqual(nrc.hosts['foo.domain.com'],
                              ('anonymous', '', 'pass'))
 
+    @unittest.skipUnless(os.name == 'posix', 'POSIX only test')
+    @unittest.skipUnless(hasattr(os, 'getuid'), "os.getuid is required")
+    @os_helper.skip_unless_working_chmod
+    def test_security_only_once(self):
+        # Make sure security check is only run once per parse when multiple
+        # entries are found.
+        check_called = netrc.netrc._security_check = Mock(return_value=True)
+
+        # Parse a default netrc with more than one password line.
+        with os_helper.temp_dir() as tmp_dir:
+            netrc_path = Path(tmp_dir) / '.netrc'
+            netrc_path.write_text("""\
+            machine foo.domain.com login bar password pass
+            machine bar.domain.com login foo password pass
+            """)
+            netrc_path.chmod(0o600)
+            with os_helper.EnvironmentVarGuard() as environ:
+                environ.set('HOME', tmp_dir)
+                netrc.netrc()
+
+        check_called.assert_called_once()
+        del check_called
+
 
 if __name__ == "__main__":
     unittest.main()