add function populate_proc

1 files changed, 39 insertions, 0 deletions

diff --git a/linuxnamespaces/__init__.py b/linuxnamespaces/__init__.py
index 2b92462..e305b4e 100644
--- a/linuxnamespaces/__init__.py
+++ b/linuxnamespaces/__init__.py
@@ -426,6 +426,45 @@ def populate_dev(
             move_mount(fd, newdev / fn)
 
 
+def populate_proc(
+    origroot: AtLocationLike,
+    newroot: PathConvertible,
+    namespaces: CloneFlags,
+) -> None:
+    """Mount a /proc hierarchy.
+
+    Note that a user with CAP_SYS_ADMIN can change read-only bind mounts.
+    Still those bind mounts provide guidance to the container as to which
+    aspects it should manage.
+    """
+    assert namespaces & CloneFlags.NEWNS == CloneFlags.NEWNS
+    newproc = AtLocation(newroot) / "proc"
+    rwns = CloneFlags.NEWPID
+    if namespaces & rwns == rwns:
+        mount(
+            "proc",
+            newproc,
+            "proc",
+            MountFlags.NOSUID | MountFlags.NODEV | MountFlags.NOEXEC,
+        )
+    else:
+        bind_mount(AtLocation(origroot) / "proc", newproc, True)
+    with _ExceptionExitCallback(umount, newproc, UmountFlags.DETACH):
+        rwns |= CloneFlags.NEWUSER | CloneFlags.NEWIPC | CloneFlags.NEWUTS
+        if namespaces & rwns != rwns:
+            psn: AtLocation | None = None
+            if namespaces & CloneFlags.NEWNET == CloneFlags.NEWNET:
+                psn = open_tree(
+                    newproc / "sys/net",
+                    OpenTreeFlags.OPEN_TREE_CLONE | OpenTreeFlags.AT_RECURSIVE,
+                )
+            bind_mount(newproc / "sys", newproc / "sys", True, True)
+            if psn is not None:
+                move_mount(psn, newproc / "sys/net")
+        elif namespaces & CloneFlags.NEWNET != CloneFlags.NEWNET:
+            bind_mount(newproc / "sys/net", newproc / "sys/net", True, True)
+
+
 def populate_sys(
     origroot: AtLocationLike,
     newroot: PathConvertible,