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collabora-online/tools/mount.cpp

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/* -*- Mode: C; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4; fill-column: 100 -*- */
/*
* Copyright the Collabora Online contributors.
*
* SPDX-License-Identifier: MPL-2.0
*
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/.
*/
/*
* This is a very tiny helper to allow overlay mounting.
*/
#include <config.h>
#include <stdio.h>
#include <errno.h>
#include <sys/mount.h>
#include <sys/stat.h>
#include <sysexits.h>
#include <unistd.h>
#include <security.h>
#ifdef __FreeBSD__
#include <stdlib.h>
#include <sys/uio.h>
#define MOUNT mount_wrapper
#define MS_MGC_VAL 0
#define MS_SILENT 0
#define MS_NODEV 0
#define MS_UNBINDABLE 0
#define MS_BIND 1
#define MS_REC 2
#define MS_REMOUNT 4
#define MS_NOATIME 8
#define MS_NOSUID 16
#define MS_RDONLY 32
void
build_iovec(struct iovec **iov, int *iovlen, const char *name, const void *val,
size_t len)
{
int i;
if (*iovlen < 0)
return;
i = *iovlen;
*iov = reinterpret_cast<struct iovec*>(realloc(*iov, sizeof **iov * (i + 2)));
if (*iov == NULL) {
*iovlen = -1;
return;
}
(*iov)[i].iov_base = strdup(name);
(*iov)[i].iov_len = strlen(name) + 1;
i++;
(*iov)[i].iov_base = const_cast<void*>(val);
if (len == (size_t)-1) {
if (val != NULL)
len = strlen(reinterpret_cast<const char*>(val)) + 1;
else
len = 0;
}
(*iov)[i].iov_len = (int)len;
*iovlen = ++i;
}
int mount_wrapper(const char *source, const char *target,
const char *filesystemtype, unsigned long mountflags,
const void *data)
{
struct iovec *iov = NULL;
int iovlen = 0;
int freebsd_flags = 0;
(void)data;
if(mountflags & MS_BIND)
filesystemtype = "nullfs";
if(mountflags & MS_REMOUNT)
freebsd_flags |= MNT_UPDATE;
if(mountflags & MS_NOATIME)
freebsd_flags |= MNT_NOATIME;
if(mountflags & MS_NOSUID)
freebsd_flags |= MNT_NOSUID;
if(mountflags & MS_RDONLY)
freebsd_flags |= MNT_RDONLY;
// TODO: handle MS_REC?
build_iovec(&iov, &iovlen, "fstype", reinterpret_cast<const void*>(filesystemtype), (size_t)-1);
build_iovec(&iov, &iovlen, "fspath", reinterpret_cast<const void*>(target), (size_t)-1);
build_iovec(&iov, &iovlen, "from", reinterpret_cast<const void*>(source), (size_t)-1);
return nmount(iov, iovlen, freebsd_flags);
}
#define MNT_DETACH 1
int umount2(const char *target, int flags)
{
struct statfs* mntbufs;
int numInfos = getmntinfo(&mntbufs, MNT_WAIT);
bool targetMounted = false;
for (int i = 0; i < numInfos; i++)
{
if (!strcmp(target, mntbufs[i].f_mntonname))
{
targetMounted = true;
break;
}
}
if (!targetMounted)
{
errno = EINVAL;
return -1;
}
if(flags == MNT_DETACH)
flags = 0;
return unmount(target, flags);
}
#else
#define MOUNT mount
#endif
void usage(const char* program)
{
fprintf(stderr, "Usage: %s <-b|-r> <source path> <target path>\n", program);
fprintf(stderr, " %s -u <target>.\n", program);
#ifdef __FreeBSD__
fprintf(stderr, " %s -d <target>.\n", program);
#endif
fprintf(stderr, " -b bind and mount the source to target.\n");
fprintf(stderr, " -r bind and mount the source to target as readonly.\n");
#ifdef __FreeBSD__
fprintf(stderr, " -d mount minimal devfs layout (random and urandom) to target.\n");
#endif
fprintf(stderr, " -u to unmount the target.\n");
}
int main(int argc, char** argv)
{
/*WARNING: PRIVILEGED CODE CHECKING START */
/*WARNING*/ if (!hasCorrectUID(/* appName = */ "coolmount"))
/*WARNING*/ {
/*WARNING*/ fprintf(stderr, "Aborting.\n");
/*WARNING*/ return EX_SOFTWARE;
/*WARNING*/ }
/*WARNING: PRIVILEGED CODE CHECKING END */
const char* program = argv[0];
if (argc < 3)
{
usage(program);
return EX_USAGE;
}
const char* option = argv[1];
if (argc == 3 && strcmp(option, "-u") == 0) // Unmount
{
const char* target = argv[2];
struct stat sb;
const bool target_exists = (stat(target, &sb) == 0 && S_ISDIR(sb.st_mode));
// Do nothing if target doesn't exist.
if (target_exists)
{
// Unmount the target, first by detaching. This should succeed.
int retval = umount2(target, MNT_DETACH);
if (retval != 0)
{
if (errno != EINVAL)
{
// Don't complain where MNT_DETACH is unsupported. Fall back to forcing instead.
fprintf(stderr, "%s: unmount failed to detach [%s]: %s.\n", program, target,
strerror(errno));
}
// Now try to force the unmounting, which isn't supported on all filesystems.
retval = umount2(target, MNT_FORCE);
if (retval != 0)
{
// From man umount(2), MNT_FORCE is not commonly supported:
// As at Linux 4.12, MNT_FORCE is supported only on the following filesystems: 9p (since
// Linux 2.6.16), ceph (since Linux 2.6.34), cifs (since Linux 2.6.12),
// fuse (since Linux 2.6.16), lustre (since Linux 3.11), and NFS (since Linux 2.1.116).
if (errno != EINVAL)
{
// Complain to capture the reason of failure.
fprintf(stderr, "%s: forced unmount of [%s] failed: %s.\n", program, target,
strerror(errno));
}
return EX_SOFTWARE;
}
}
}
}
#ifdef __FreeBSD__
else if (argc == 3 && strcmp(option, "-d") == 0) // Mount devfs
{
const char* target = argv[2];
struct stat sb;
const bool target_exists = (stat(target, &sb) == 0 && S_ISDIR(sb.st_mode));
if (!target_exists)
{
fprintf(stderr, "%s: cannot mount on invalid target directory [%s].\n", program,
target);
return EX_USAGE;
}
struct iovec *iov = NULL;
int iovlen = 0;
build_iovec(&iov, &iovlen, "fstype", "devfs", (size_t)-1);
build_iovec(&iov, &iovlen, "fspath", reinterpret_cast<const void*>(target), (size_t)-1);
build_iovec(&iov, &iovlen, "from", "devfs", (size_t)-1);
// See /etc/defaults/devfs.rules
// [devfsrules_jail=4]
build_iovec(&iov, &iovlen, "ruleset", "4", (size_t)-1);
int retval = nmount(iov, iovlen, 0);
if (retval)
{
fprintf(stderr, "%s: mount failed create to devfs layout in [%s]: %s.\n", program, target,
strerror(errno));
return EX_SOFTWARE;
}
}
#endif
else if (argc == 4) // Mount
{
const char* source = argv[2];
struct stat sb;
if (stat(source, &sb))
{
fprintf(stderr, "%s: cannot mount from invalid source [%s]. stat failed with %s\n",
program, source, strerror(errno));
return EX_USAGE;
}
const bool isDir = S_ISDIR(sb.st_mode);
const bool isCharDev = S_ISCHR(sb.st_mode); // We don't support regular files.
if (isCharDev)
{
// Even for character devices, we only support the random devices.
if (strstr("/dev/random", source) && strstr("/dev/urandom", source))
{
fprintf(stderr, "%s: cannot mount untrusted character-device [%s]", program,
source);
return EX_USAGE;
}
}
if (!isDir && !isCharDev)
{
fprintf(stderr,
"%s: cannot mount from invalid source [%s], it is neither a file nor a "
"directory.\n",
program, source);
return EX_USAGE;
}
const char* target = argv[3];
if (stat(target, &sb))
{
fprintf(stderr, "%s: cannot mount on invalid target [%s]. stat failed with %s\n",
program, target, strerror(errno));
return EX_USAGE;
}
const bool target_exists =
((isDir && S_ISDIR(sb.st_mode)) || (isCharDev && S_ISREG(sb.st_mode)));
if (!target_exists)
{
fprintf(stderr,
"%s: cannot mount on invalid target [%s], it is not a %s as the source\n",
program, target, isDir ? "directory" : "file");
return EX_USAGE;
}
// Mount the source path as the target path.
// First bind to mount an existing directory node into the chroot.
// MS_BIND ignores other flags.
if (strcmp(option, "-b") == 0) // Shared or Bind Mount.
{
const int retval
= MOUNT(source, target, nullptr, (MS_MGC_VAL | MS_BIND | MS_REC), nullptr);
if (retval)
{
fprintf(stderr, "%s: mount failed to bind [%s] to [%s]: %s.\n", program, source,
target, strerror(errno));
return EX_SOFTWARE;
}
}
else if (strcmp(option, "-r") == 0) // Readonly Mount.
{
// Now we need to set read-only and other flags with a remount.
int retval = MOUNT(source, target, nullptr,
(MS_BIND | MS_REC | MS_REMOUNT | MS_NOATIME | MS_NODEV | MS_NOSUID
| MS_RDONLY | MS_SILENT),
nullptr);
if (retval)
{
fprintf(stderr, "%s: mount failed remount [%s] readonly: %s.\n", program, target,
strerror(errno));
return EX_SOFTWARE;
}
retval = MOUNT(source, target, nullptr, (MS_UNBINDABLE | MS_REC), nullptr);
if (retval)
{
fprintf(stderr, "%s: mount failed make [%s] private: %s.\n", program, target,
strerror(errno));
return EX_SOFTWARE;
}
}
}
else
{
usage(program);
return EX_USAGE;
}
fflush(stderr);
return EX_OK;
}
/* vim:set shiftwidth=4 softtabstop=4 expandtab: */
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