regression_pidfd_setns_test.c

  1// SPDX-License-Identifier: GPL-2.0
  2#define _GNU_SOURCE
  3#include <errno.h>
  4#include <sched.h>
  5#include <signal.h>
  6#include <stdio.h>
  7#include <stdlib.h>
  8#include <string.h>
  9#include <sys/socket.h>
 10#include <unistd.h>
 11#include "../pidfd/pidfd.h"
 12#include "../kselftest_harness.h"
 13
 14/*
 15 * Regression tests for the setns(pidfd) active reference counting bug.
 16 *
 17 * These tests are based on the reproducers that triggered the race condition
 18 * fixed by commit 1c465d0518dc ("ns: handle setns(pidfd, ...) cleanly").
 19 *
 20 * The bug: When using setns() with a pidfd, if the target task exits between
 21 * prepare_nsset() and commit_nsset(), the namespaces would become inactive.
 22 * Then ns_ref_active_get() would increment from 0 without properly resurrecting
 23 * the owner chain, causing active reference count underflows.
 24 */
 25
 26/*
 27 * Simple pidfd setns test using create_child()+unshare().
 28 *
 29 * Without the fix, this would trigger active refcount warnings when the
 30 * parent exits after doing setns(pidfd) on a child that has already exited.
 31 */
 32TEST(simple_pidfd_setns)
 33{
 34	pid_t child_pid;
 35	int pidfd = -1;
 36	int ret;
 37	int sv[2];
 38	char c;
 39
 40	/* Ignore SIGCHLD for autoreap */
 41	ASSERT_NE(signal(SIGCHLD, SIG_IGN), SIG_ERR);
 42
 43	ASSERT_EQ(socketpair(AF_UNIX, SOCK_STREAM, 0, sv), 0);
 44
 45	/* Create a child process without namespaces initially */
 46	child_pid = create_child(&pidfd, 0);
 47	ASSERT_GE(child_pid, 0);
 48
 49	if (child_pid == 0) {
 50		close(sv[0]);
 51
 52		if (unshare(CLONE_NEWUTS | CLONE_NEWIPC | CLONE_NEWNET | CLONE_NEWUSER) < 0) {
 53			close(sv[1]);
 54			_exit(1);
 55		}
 56
 57		/* Signal parent that namespaces are ready */
 58		if (write_nointr(sv[1], "1", 1) < 0) {
 59			close(sv[1]);
 60			_exit(1);
 61		}
 62
 63		close(sv[1]);
 64		_exit(0);
 65	}
 66	ASSERT_GE(pidfd, 0);
 67	EXPECT_EQ(close(sv[1]), 0);
 68
 69	ret = read_nointr(sv[0], &c, 1);
 70	ASSERT_EQ(ret, 1);
 71	EXPECT_EQ(close(sv[0]), 0);
 72
 73	/* Set to child's namespaces via pidfd */
 74	ret = setns(pidfd, CLONE_NEWUTS | CLONE_NEWIPC);
 75	TH_LOG("setns() returned %d", ret);
 76	close(pidfd);
 77}
 78
 79/*
 80 * Simple pidfd setns test using create_child().
 81 *
 82 * This variation uses create_child() with namespace flags directly.
 83 * Namespaces are created immediately at clone time.
 84 */
 85TEST(simple_pidfd_setns_clone)
 86{
 87	pid_t child_pid;
 88	int pidfd = -1;
 89	int ret;
 90
 91	/* Ignore SIGCHLD for autoreap */
 92	ASSERT_NE(signal(SIGCHLD, SIG_IGN), SIG_ERR);
 93
 94	/* Create a child process with new namespaces using create_child() */
 95	child_pid = create_child(&pidfd, CLONE_NEWUSER | CLONE_NEWUTS | CLONE_NEWIPC | CLONE_NEWNET);
 96	ASSERT_GE(child_pid, 0);
 97
 98	if (child_pid == 0) {
 99		/* Child: sleep for a while so parent can setns to us */
100		sleep(2);
101		_exit(0);
102	}
103
104	/* Parent: pidfd was already created by create_child() */
105	ASSERT_GE(pidfd, 0);
106
107	/* Set to child's namespaces via pidfd */
108	ret = setns(pidfd, CLONE_NEWUTS | CLONE_NEWIPC);
109	close(pidfd);
110	TH_LOG("setns() returned %d", ret);
111}
112
113TEST_HARNESS_MAIN