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/* SPDX-License-Identifier: LGPL-2.1+ */
/*
* Copyright (c) 2021 Christian Brauner <christian.brauner@ubuntu.com>
* All Rights Reserved.
*
* Regression test to verify that creating a series of detached mounts,
* attaching them to the filesystem, and unmounting them does not trigger an
* integer overflow in ns->mounts causing the kernel to block any new mounts in
* count_mounts() and returning ENOSPC because it falsely assumes that the
* maximum number of mounts in the mount namespace has been reached, i.e. it
* thinks it can't fit the new mounts into the mount namespace anymore.
*/
#include <errno.h>
#include <fcntl.h>
#include <getopt.h>
#include <limits.h>
#include <sched.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mount.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>
#include "vfs/missing.h"
static bool is_shared_mountpoint(const char *path)
{
bool shared = false;
FILE *f = NULL;
char *line = NULL;
int i;
size_t len = 0;
f = fopen("/proc/self/mountinfo", "re");
if (!f)
return 0;
while (getline(&line, &len, f) > 0) {
char *slider1, *slider2;
for (slider1 = line, i = 0; slider1 && i < 4; i++)
slider1 = strchr(slider1 + 1, ' ');
if (!slider1)
continue;
slider2 = strchr(slider1 + 1, ' ');
if (!slider2)
continue;
*slider2 = '\0';
if (strcmp(slider1 + 1, path) == 0) {
/* This is the path. Is it shared? */
slider1 = strchr(slider2 + 1, ' ');
if (slider1 && strstr(slider1, "shared:")) {
shared = true;
break;
}
}
}
fclose(f);
free(line);
return shared;
}
static void usage(void)
{
const char *text = "mount-new [--recursive] <base-dir>\n";
fprintf(stderr, "%s", text);
_exit(EXIT_SUCCESS);
}
#define exit_usage(format, ...) \
({ \
fprintf(stderr, format "\n", ##__VA_ARGS__); \
usage(); \
})
#define exit_log(format, ...) \
({ \
fprintf(stderr, format "\n", ##__VA_ARGS__); \
exit(EXIT_FAILURE); \
})
static const struct option longopts[] = {
{"help", no_argument, 0, 'a'},
{ NULL, no_argument, 0, 0 },
};
int main(int argc, char *argv[])
{
int exit_code = EXIT_SUCCESS, index = 0;
int dfd, fd_tree, new_argc, ret, i;
char *base_dir;
char *const *new_argv;
char target[PATH_MAX];
while ((ret = getopt_long_only(argc, argv, "", longopts, &index)) != -1) {
switch (ret) {
case 'a':
/* fallthrough */
default:
usage();
}
}
new_argv = &argv[optind];
new_argc = argc - optind;
if (new_argc < 1)
exit_usage("Missing base directory\n");
base_dir = new_argv[0];
if (*base_dir != '/')
exit_log("Please specify an absolute path");
/* Ensure that target is a shared mountpoint. */
if (!is_shared_mountpoint(base_dir))
exit_log("Please ensure that \"%s\" is a shared mountpoint", base_dir);
ret = unshare(CLONE_NEWNS);
if (ret < 0)
exit_log("%m - Failed to create new mount namespace");
ret = mount(NULL, base_dir, NULL, MS_REC | MS_SHARED, NULL);
if (ret < 0)
exit_log("%m - Failed to make base_dir shared mountpoint");
dfd = open(base_dir, O_RDONLY | O_DIRECTORY | O_CLOEXEC);
if (dfd < 0)
exit_log("%m - Failed to open base directory \"%s\"", base_dir);
ret = mkdirat(dfd, "detached-move-mount", 0755);
if (ret < 0)
exit_log("%m - Failed to create required temporary directories");
ret = snprintf(target, sizeof(target), "%s/detached-move-mount", base_dir);
if (ret < 0 || (size_t)ret >= sizeof(target))
exit_log("%m - Failed to assemble target path");
/*
* Having a mount table with 10000 mounts is already quite excessive
* and shoult account even for weird test systems.
*/
for (i = 0; i < 10000; i++) {
fd_tree = sys_open_tree(dfd, "detached-move-mount",
OPEN_TREE_CLONE |
OPEN_TREE_CLOEXEC |
AT_EMPTY_PATH);
if (fd_tree < 0) {
if (errno == ENOSYS) /* New mount API not (fully) supported. */
break;
fprintf(stderr, "%m - Failed to open %d(detached-move-mount)", dfd);
exit_code = EXIT_FAILURE;
break;
}
ret = sys_move_mount(fd_tree, "", dfd, "detached-move-mount", MOVE_MOUNT_F_EMPTY_PATH);
if (ret < 0) {
if (errno == ENOSPC)
fprintf(stderr, "%m - Buggy mount counting");
else if (errno == ENOSYS) /* New mount API not (fully) supported. */
break;
else
fprintf(stderr, "%m - Failed to attach mount to %d(detached-move-mount)", dfd);
exit_code = EXIT_FAILURE;
break;
}
close(fd_tree);
ret = umount2(target, MNT_DETACH);
if (ret < 0) {
fprintf(stderr, "%m - Failed to unmount %s", target);
exit_code = EXIT_FAILURE;
break;
}
}
(void)unlinkat(dfd, "detached-move-mount", AT_REMOVEDIR);
close(dfd);
exit(exit_code);
}
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