samples/vfs/test-list-all-mounts.c

// SPDX-License-Identifier: GPL-2.0-or-later
// Copyright (c) 2024 Christian Brauner <brauner@kernel.org>

#define _GNU_SOURCE
#include <errno.h>
#include <limits.h>
#include <linux/types.h>
#include <inttypes.h>
#include <stdio.h>

#include "../../tools/testing/selftests/pidfd/pidfd.h"
#include "samples-vfs.h"

static int __statmount(__u64 mnt_id, __u64 mnt_ns_id, __u64 mask,
		       struct statmount *stmnt, size_t bufsize,
		       unsigned int flags)
{
	struct mnt_id_req req = {
		.size		= MNT_ID_REQ_SIZE_VER1,
		.mnt_id		= mnt_id,
		.param		= mask,
		.mnt_ns_id	= mnt_ns_id,
	};

	return syscall(__NR_statmount, &req, stmnt, bufsize, flags);
}

static struct statmount *sys_statmount(__u64 mnt_id, __u64 mnt_ns_id,
				       __u64 mask, unsigned int flags)
{
	size_t bufsize = 1 << 15;
	struct statmount *stmnt = NULL, *tmp = NULL;
	int ret;

	for (;;) {
		tmp = realloc(stmnt, bufsize);
		if (!tmp)
			goto out;

		stmnt = tmp;
		ret = __statmount(mnt_id, mnt_ns_id, mask, stmnt, bufsize, flags);
		if (!ret)
			return stmnt;

		if (errno != EOVERFLOW)
			goto out;

		bufsize <<= 1;
		if (bufsize >= UINT_MAX / 2)
			goto out;
	}

out:
	free(stmnt);
	return NULL;
}

static ssize_t sys_listmount(__u64 mnt_id, __u64 last_mnt_id, __u64 mnt_ns_id,
			     __u64 list[], size_t num, unsigned int flags)
{
	struct mnt_id_req req = {
		.size		= MNT_ID_REQ_SIZE_VER1,
		.mnt_id		= mnt_id,
		.param		= last_mnt_id,
		.mnt_ns_id	= mnt_ns_id,
	};

	return syscall(__NR_listmount, &req, list, num, flags);
}

int main(int argc, char *argv[])
{
#define LISTMNT_BUFFER 10
	__u64 list[LISTMNT_BUFFER], last_mnt_id = 0;
	int ret, pidfd, fd_mntns;
	struct mnt_ns_info info = {};

	pidfd = sys_pidfd_open(getpid(), 0);
	if (pidfd < 0)
		die_errno("pidfd_open failed");

	fd_mntns = ioctl(pidfd, PIDFD_GET_MNT_NAMESPACE, 0);
	if (fd_mntns < 0)
		die_errno("ioctl(PIDFD_GET_MNT_NAMESPACE) failed");

	ret = ioctl(fd_mntns, NS_MNT_GET_INFO, &info);
	if (ret < 0)
		die_errno("ioctl(NS_GET_MNTNS_ID) failed");

	printf("Listing %u mounts for mount namespace %" PRIu64 "\n",
	       info.nr_mounts, (uint64_t)info.mnt_ns_id);
	for (;;) {
		ssize_t nr_mounts;
next:
		nr_mounts = sys_listmount(LSMT_ROOT, last_mnt_id,
					  info.mnt_ns_id, list, LISTMNT_BUFFER,
					  0);
		if (nr_mounts <= 0) {
			int fd_mntns_next;

			printf("Finished listing %u mounts for mount namespace %" PRIu64 "\n\n",
			       info.nr_mounts, (uint64_t)info.mnt_ns_id);
			fd_mntns_next = ioctl(fd_mntns, NS_MNT_GET_NEXT, &info);
			if (fd_mntns_next < 0) {
				if (errno == ENOENT) {
					printf("Finished listing all mount namespaces\n");
					exit(0);
				}
				die_errno("ioctl(NS_MNT_GET_NEXT) failed");
			}
			close(fd_mntns);
			fd_mntns = fd_mntns_next;
			last_mnt_id = 0;
			printf("Listing %u mounts for mount namespace %" PRIu64 "\n",
			       info.nr_mounts, (uint64_t)info.mnt_ns_id);
			goto next;
		}

		for (size_t cur = 0; cur < nr_mounts; cur++) {
			struct statmount *stmnt;

			last_mnt_id = list[cur];

			stmnt = sys_statmount(last_mnt_id, info.mnt_ns_id,
					      STATMOUNT_SB_BASIC |
					      STATMOUNT_MNT_BASIC |
					      STATMOUNT_MNT_ROOT |
					      STATMOUNT_MNT_POINT |
					      STATMOUNT_MNT_NS_ID |
					      STATMOUNT_MNT_OPTS |
					      STATMOUNT_FS_TYPE |
					      STATMOUNT_MNT_UIDMAP |
					      STATMOUNT_MNT_GIDMAP, 0);
			if (!stmnt) {
				printf("Failed to statmount(%" PRIu64 ") in mount namespace(%" PRIu64 ")\n",
				       (uint64_t)last_mnt_id, (uint64_t)info.mnt_ns_id);
				continue;
			}

			printf("mnt_id:\t\t%" PRIu64 "\nmnt_parent_id:\t%" PRIu64 "\nfs_type:\t%s\nmnt_root:\t%s\nmnt_point:\t%s\nmnt_opts:\t%s\n",
			       (uint64_t)stmnt->mnt_id,
			       (uint64_t)stmnt->mnt_parent_id,
			       (stmnt->mask & STATMOUNT_FS_TYPE)   ? stmnt->str + stmnt->fs_type   : "",
			       (stmnt->mask & STATMOUNT_MNT_ROOT)  ? stmnt->str + stmnt->mnt_root  : "",
			       (stmnt->mask & STATMOUNT_MNT_POINT) ? stmnt->str + stmnt->mnt_point : "",
			       (stmnt->mask & STATMOUNT_MNT_OPTS)  ? stmnt->str + stmnt->mnt_opts  : "");

			if (stmnt->mask & STATMOUNT_MNT_UIDMAP) {
				const char *idmap = stmnt->str + stmnt->mnt_uidmap;

				for (size_t idx = 0; idx < stmnt->mnt_uidmap_num; idx++) {
					printf("mnt_uidmap[%zu]:\t%s\n", idx, idmap);
					idmap += strlen(idmap) + 1;
				}
			}

			if (stmnt->mask & STATMOUNT_MNT_GIDMAP) {
				const char *idmap = stmnt->str + stmnt->mnt_gidmap;

				for (size_t idx = 0; idx < stmnt->mnt_gidmap_num; idx++) {
					printf("mnt_gidmap[%zu]:\t%s\n", idx, idmap);
					idmap += strlen(idmap) + 1;
				}
			}

			printf("\n");

			free(stmnt);
		}
	}

	exit(0);
}