From e6d2aa979cea1a4d98f588a66b01d742f685971a Mon Sep 17 00:00:00 2001
From: Helmut Grohne <helmut@subdivi.de>
Date: Wed, 13 Aug 2025 11:03:08 +0200
Subject: support parsing /etc/sub?id files keyed on UID

Link: https://bugs.debian.org/1110876
---
 linuxnamespaces/idmap.py | 34 ++++++++++++++++++++++++++++------
 1 file changed, 28 insertions(+), 6 deletions(-)

diff --git a/linuxnamespaces/idmap.py b/linuxnamespaces/idmap.py
index d9cf0eb..f66456d 100644
--- a/linuxnamespaces/idmap.py
+++ b/linuxnamespaces/idmap.py
@@ -7,7 +7,7 @@ namespace.
 
 import bisect
 import dataclasses
-import getpass
+import pwd
 import os
 import subprocess
 import typing
@@ -16,17 +16,36 @@ from .atlocation import AtLocation, AtLocationLike
 
 
 def subidranges(
-    kind: typing.Literal["uid", "gid"], login: str | None = None
+    kind: typing.Literal["uid", "gid"],
+    login: str | None = None,
+    uid: int | None = None,
 ) -> typing.Iterator[tuple[int, int]]:
     """Parse a `/etc/sub?id` file for ranges allocated to the given or current
     user. Return all ranges as (start, count) pairs.
     """
+    if uid is None:
+        if login is None:
+            uid = os.getuid()
+        else:
+            try:
+                uid = pwd.getpwnam(login).pw_uid
+            except KeyError:
+                pass
     if login is None:
-        login = getpass.getuser()
+        try:
+            login = pwd.getpwuid(uid).pw_name
+        except KeyError:
+            pass
     with open(f"/etc/sub{kind}") as filelike:
         for line in filelike:
             parts = line.strip().split(":")
-            if parts[0] == login:
+            try:
+                curuid = int(parts[0])
+            except ValueError:
+                curuid = None
+            if (login is not None and parts[0] == login) or (
+                curuid is not None and uid is not None and curuid == uid
+            ):
                 yield (int(parts[1]), int(parts[2]))
 
 
@@ -95,13 +114,16 @@ class IDAllocation:
 
     @classmethod
     def loadsubid(
-        cls, kind: typing.Literal["uid", "gid"], login: str | None = None,
+        cls,
+        kind: typing.Literal["uid", "gid"],
+        login: str | None = None,
+        uid: int | None = None,
     ) -> "IDAllocation":
         """Load a `/etc/sub?id` file and return ids allocated to the given
         login or current user.
         """
         self = cls()
-        for start, count in subidranges(kind, login):
+        for start, count in subidranges(kind, login, uid):
             self.add_range(start, count)
         return self
 
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