tools/testing/selftests/core/unshare_test.c

// SPDX-License-Identifier: GPL-2.0

#define _GNU_SOURCE
#include <errno.h>
#include <fcntl.h>
#include <linux/kernel.h>
#include <limits.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <syscall.h>
#include <unistd.h>
#include <sys/resource.h>
#include <linux/close_range.h>

#include "kselftest_harness.h"
#include "../clone3/clone3_selftests.h"

TEST(unshare_EMFILE)
{
	pid_t pid;
	int status;
	struct __clone_args args = {
		.flags = CLONE_FILES,
		.exit_signal = SIGCHLD,
	};
	int fd;
	ssize_t n, n2;
	static char buf[512], buf2[512];
	struct rlimit rlimit;
	int nr_open;

	fd = open("/proc/sys/fs/nr_open", O_RDWR);
	ASSERT_GE(fd, 0);

	n = read(fd, buf, sizeof(buf));
	ASSERT_GT(n, 0);
	ASSERT_EQ(buf[n - 1], '\n');

	ASSERT_EQ(sscanf(buf, "%d", &nr_open), 1);

	/*
	 * Cap nr_open for the duration of the test to avoid ENOMEM from a
	 * huge fd table allocation; buf/n keep the real original value so
	 * fs.nr_open can be restored to it once the test is done.
	 */
	if (nr_open > 1024 * 1024)
		nr_open = 1024 * 1024;

	ASSERT_EQ(0, getrlimit(RLIMIT_NOFILE, &rlimit));

	/* bump fs.nr_open */
	n2 = sprintf(buf2, "%d\n", nr_open + 1024);
	lseek(fd, 0, SEEK_SET);
	write(fd, buf2, n2);

	/* bump ulimit -n */
	rlimit.rlim_cur = nr_open + 1024;
	rlimit.rlim_max = nr_open + 1024;
	EXPECT_EQ(0, setrlimit(RLIMIT_NOFILE, &rlimit)) {
		lseek(fd, 0, SEEK_SET);
		write(fd, buf, n);
		exit(EXIT_FAILURE);
	}

	/* get a descriptor past the old fs.nr_open */
	EXPECT_GE(dup2(2, nr_open + 64), 0) {
		lseek(fd, 0, SEEK_SET);
		write(fd, buf, n);
		exit(EXIT_FAILURE);
	}

	/* get descriptor table shared */
	pid = sys_clone3(&args, sizeof(args));
	EXPECT_GE(pid, 0) {
		lseek(fd, 0, SEEK_SET);
		write(fd, buf, n);
		exit(EXIT_FAILURE);
	}

	if (pid == 0) {
		int err;
		char buf3[32];
		ssize_t n3;

		/* restore fs.nr_open to the (possibly capped) test baseline */
		n3 = sprintf(buf3, "%d\n", nr_open);
		lseek(fd, 0, SEEK_SET);
		write(fd, buf3, n3);
		/* ... and now unshare(CLONE_FILES) must fail with EMFILE */
		err = unshare(CLONE_FILES);
		EXPECT_EQ(err, -1)
			exit(EXIT_FAILURE);
		EXPECT_EQ(errno, EMFILE)
			exit(EXIT_FAILURE);
		exit(EXIT_SUCCESS);
	}

	EXPECT_EQ(waitpid(pid, &status, 0), pid);
	EXPECT_EQ(true, WIFEXITED(status));
	EXPECT_EQ(0, WEXITSTATUS(status));

	/* restore the real fs.nr_open value */
	lseek(fd, 0, SEEK_SET);
	write(fd, buf, n);
}

TEST_HARNESS_MAIN