add function for prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_RAISE, ...)

2 files changed, 29 insertions, 11 deletions

diff --git a/examples/withallsubuids.py b/examples/withallsubuids.py
index ead0482..3bed3bc 100755
--- a/examples/withallsubuids.py
+++ b/examples/withallsubuids.py
@@ -43,15 +43,7 @@ def main() -> None:
     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.prctl(
-            47,  # PR_CAP_AMBIENT
-            2,  # PR_CAP_AMBIENT_RAISE
-            cap.bit_length() - 1,
-        )
+    linuxnamespaces.prctl_raise_ambient_capabilities(capabilities.inheritable)
     if len(sys.argv) > 1:
         os.execvp(sys.argv[1], sys.argv[1:])
     else:
diff --git a/linuxnamespaces/syscalls.py b/linuxnamespaces/syscalls.py
index c22a9d8..8f5e25b 100644
--- a/linuxnamespaces/syscalls.py
+++ b/linuxnamespaces/syscalls.py
@@ -337,6 +337,12 @@ class OpenTreeFlags(enum.IntFlag):
     )
 
 
+class PrctlOption(enum.IntEnum):
+    """This value may be supplied to prctl(2) as option."""
+
+    PR_CAP_AMBIENT = 47
+
+
 class UmountFlags(enum.IntFlag):
     """This value may be supplied to umount2(2) as flags."""
 
@@ -622,11 +628,31 @@ def pivot_root(new_root: PathConvertible, put_old: PathConvertible) -> None:
     """Python wrapper for pivot_root(2)."""
     call_libc("pivot_root", os.fsencode(new_root), os.fsencode(put_old))
 
+
 def prctl(
-    option: int, arg2: int = 0, arg3: int = 0, arg4: int = 0, arg5: int = 0
+    option: PrctlOption | int,
+    arg2: int = 0,
+    arg3: int = 0,
+    arg4: int = 0,
+    arg5: int = 0,
 ) -> int:
     """Python wrapper for prctl(2)."""
-    return call_libc("prctl", option, arg2, arg3, arg4, arg5)
+    return call_libc("prctl", int(option), arg2, arg3, arg4, arg5)
+
+
+def prctl_raise_ambient_capabilities(capabilities: int) -> None:
+    """Raise all ambient capabilities in the given bitfield. If multiple bits
+    are set, this results in multiple prctl(2) syscalls.
+    """
+    while capabilities:
+        cap = capabilities & (~capabilities + 1)
+        capabilities ^= cap
+        prctl(
+            PrctlOption.PR_CAP_AMBIENT,
+            2,  # PR_CAP_AMBIENT_RAISE
+            cap.bit_length() - 1,
+        )
+
 
 def setns(fd: int, nstype: CloneFlags = CloneFlags.NONE) -> None:
     """Python wrapper for setns(2)."""