mount.c

/*

   nsjail - CLONE_NEWNS routines
   -----------------------------------------

   Copyright 2014 Google Inc. All Rights Reserved.

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

     http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.

*/

#include "mount.h"

#include <errno.h>
#include <fcntl.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <sys/mount.h>
#include <sys/stat.h>
#include <sys/statvfs.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>

#include "log.h"

static bool mountIsDir(const char *path)
{
	if (path == NULL || strcmp(path, "none") == 0) {
		return false;
	}
	struct stat st;
	if (stat(path, &st) == -1) {
		PLOG_E("stat('%s')", path);
		return false;
	}
	if (S_ISDIR(st.st_mode)) {
		return true;
	}
	return false;
}

// It's a not a simple reversal of containIsDir() as it returns also 'false' upon
// stat() failure
static bool mountNotIsDir(const char *path)
{
	if (path == NULL || strcmp(path, "none") == 0) {
		return false;
	}
	struct stat st;
	if (stat(path, &st) == -1) {
		PLOG_E("stat('%s')", path);
		return false;
	}
	if (S_ISDIR(st.st_mode)) {
		return false;
	}
	return true;
}

static bool mountMount(struct nsjconf_t *nsjconf, struct mounts_t *mpt, const char *dst)
{
	LOG_D("Mounting '%s' on '%s' (type:'%s', flags:0x%tx)", mpt->src, dst, mpt->fs_type,
	      mpt->flags);

	if (mountIsDir(mpt->src) == true) {
		if (mkdir(dst, 0711) == -1 && errno != EEXIST) {
			PLOG_W("mkdir('%s')", dst);
		}
	}

	if (mountNotIsDir(mpt->src) == true) {
		int fd = open(dst, O_CREAT | O_RDONLY, 0644);
		if (fd >= 0) {
			close(fd);
		} else {
			PLOG_W("open('%s', O_CREAT|O_RDONLY, 0700)", dst);
		}
	}

	if (mount(mpt->src, dst, mpt->fs_type, mpt->flags, mpt->options) == -1) {
		if (errno == EACCES) {
			PLOG_E
			    ("mount('%s', '%s', type='%s') failed. Try fixing this problem by applying 'chmod o+x' to the '%s' directory and its ancestors",
			     mpt->src, dst, mpt->fs_type, nsjconf->chroot);
		} else {
			PLOG_E("mount('%s', '%s', type='%s') failed", mpt->src, dst, mpt->fs_type);
		}
		return false;
	}
	return true;
}

static bool mountRemountRO(struct mounts_t *mpt)
{
	struct statvfs vfs;
	if (statvfs(mpt->dst, &vfs) == -1) {
		PLOG_E("statvfs('%s')", mpt->dst);
		return false;
	}

	if (mpt->flags & MS_RDONLY) {
		LOG_D("Re-mounting RO '%s'", mpt->dst);
		/*
		 * It's fine to use 'flags | vfs.f_flag' here as per
		 * /usr/include/x86_64-linux-gnu/bits/statvfs.h: 'Definitions for
		 * the flag in `f_flag'.  These definitions should be
		 * kept in sync with the definitions in <sys/mount.h>'
		 */
		if (mount
		    (mpt->dst, mpt->dst, NULL,
		     MS_BIND | MS_REMOUNT | MS_RDONLY | vfs.f_flag, 0) == -1) {
			PLOG_E("mount('%s', MS_REC|MS_BIND|MS_REMOUNT|MS_RDONLY)", mpt->dst);
			return false;
		}
	}
	return true;
}

bool mountInitNs(struct nsjconf_t * nsjconf)
{
	if (nsjconf->clone_newns == false) {
		if (chroot(nsjconf->chroot) == -1) {
			PLOG_E("chroot('%s')", nsjconf->chroot) {
				return false;
			}
		}
		if (chdir("/") == -1) {
			PLOG_E("chdir('/')");
			return false;
		}
		return true;
	}

	const char *const destdir = "/tmp";
	if (mount("none", destdir, "tmpfs", 0, NULL) == -1) {
		PLOG_E("mount('%s', 'tmpfs'", destdir);
		return false;
	}
	char newrootdir[PATH_MAX];
	snprintf(newrootdir, sizeof(newrootdir), "%s/%s", destdir, "new_root");
	if (mkdir(newrootdir, 0755) == -1) {
		PLOG_E("mkdir('%s')", newrootdir);
		return false;
	}

	struct mounts_t *p;
	TAILQ_FOREACH(p, &nsjconf->mountpts, pointers) {
		char dst[PATH_MAX];
		snprintf(dst, sizeof(dst), "%s/%s", newrootdir, p->dst);
		if (mountMount(nsjconf, p, dst) == false) {
			return false;
		}
	}

	char pivotrootdir[PATH_MAX];
	snprintf(pivotrootdir, sizeof(pivotrootdir), "%s/%s", destdir, "pivot_root");
	if (mkdir(pivotrootdir, 0755) == -1) {
		PLOG_E("mkdir('%s')", pivotrootdir);
		return false;
	}
	if (syscall(__NR_pivot_root, destdir, pivotrootdir) == -1) {
		PLOG_E("pivot_root('%s', '%s')", destdir, pivotrootdir);
		return false;
	}
	if (umount2("/pivot_root", MNT_DETACH) == -1) {
		PLOG_E("umount2('/pivot_root', MNT_DETACH)");
		return false;
	}
	if (chroot("/new_root") == -1) {
		PLOG_E("CHROOT('/new_root')");
		return false;
	}

	if (chdir(nsjconf->cwd) == -1) {
		PLOG_E("chdir('%s')", nsjconf->cwd);
		return false;
	}

	TAILQ_FOREACH(p, &nsjconf->mountpts, pointers) {
		if (mountRemountRO(p) == false) {
			return false;
		}
	}

	/*
	 * Remove the tmpfs from /tmp is we are mounting / as root
	 */
	if (0 == strcmp(nsjconf->chroot, "/")) {
		if (umount2(destdir, MNT_DETACH) == -1) {
			PLOG_W("umount2('%s', MNT_DETACH) failed", destdir);
		}
	}

	return true;
}