add withallsubuids.py example

1 files changed, 65 insertions, 0 deletions

diff --git a/examples/withallsubuids.py b/examples/withallsubuids.py
new file mode 100755
index 0000000..8b90e9a
--- /dev/null
+++ b/examples/withallsubuids.py
@@ -0,0 +1,65 @@
+#!/usr/bin/python3
+# Copyright 2024 Helmut Grohne <helmut@subdivi.de>
+# SPDX-License-Identifier: GPL-3
+
+"""Map all available ranges from /etc/subuid and /etc/subgid as identity and
+run a given command with all capabilities (including CAP_DAC_OVERRIDE)
+inherited.
+"""
+
+import os
+import sys
+
+if __file__.split("/")[-2:-1] == ["examples"]:
+    sys.path.insert(0, "/".join(__file__.split("/")[:-2]))
+
+import linuxnamespaces
+
+
+def main() -> None:
+    # Construct an identity mapping of all available user/group ids
+    uidmap = [
+        linuxnamespaces.IDMapping(os.getuid(), os.getuid(), 1),
+        *(
+            linuxnamespaces.IDMapping(start, start, count)
+            for start, count
+            in linuxnamespaces.IDAllocation.loadsubid("uid").ranges
+        ),
+    ]
+    gidmap = [
+        linuxnamespaces.IDMapping(os.getgid(), os.getgid(), 1),
+        *(
+            linuxnamespaces.IDMapping(start, start, count)
+            for start, count
+            in linuxnamespaces.IDAllocation.loadsubid("gid").ranges
+        ),
+    ]
+    linuxnamespaces.unshare_user_idmap(uidmap, gidmap)
+
+    # We haven't changed uid. We still are non-root, but the user namespace
+    # augmented our permitted and effective capabilities! Add them to the
+    # inheritable set.
+    capabilities = linuxnamespaces.CapabilitySets.get()
+    capabilities.inheritable = capabilities.permitted & capabilities.effective
+    capabilities.set()
+    # Add all inheritable capabilities to the ambient set.
+    caps = capabilities.inheritable
+    while caps:
+        cap = caps & (~caps + 1)
+        caps ^= cap
+        linuxnamespaces.call_libc(
+            "prctl",
+            47,  # PR_CAP_AMBIENT
+            2,  # PR_CAP_AMBIENT_RAISE
+            cap.bit_length() - 1,
+            0,
+            0,
+        )
+    if len(sys.argv) > 1:
+        os.execvp(sys.argv[1], sys.argv[1:])
+    else:
+        os.execvp(os.environ["SHELL"], [os.environ["SHELL"]])
+
+
+if __name__ == "__main__":
+    main()