/* SPDX-License-Identifier: LGPL-2.1-or-later */
/*
* This file is part of libmount from util-linux project.
*
* Copyright (C) 2011-2018 Karel Zak <kzak@redhat.com>
*
* libmount is free software; you can redistribute it and/or modify it
* under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation; either version 2.1 of the License, or
* (at your option) any later version.
*/
/*
* DOCS: - "lo@" prefix for fstype is unsupported
*/
#include <blkid.h>
#include <stdbool.h>
#include "mountP.h"
#include "loopdev.h"
#include "linux_version.h"
int mnt_context_is_loopdev(struct libmnt_context *cxt)
{
const char *type, *src;
assert(cxt);
/* The mount flags have to be merged, otherwise we have to use
* expensive mnt_context_get_user_mflags() instead of cxt->user_mountflags. */
assert((cxt->flags & MNT_FL_MOUNTFLAGS_MERGED));
if (!cxt->fs)
return 0;
src = mnt_fs_get_srcpath(cxt->fs);
if (!src)
return 0; /* backing file not set */
if (cxt->user_mountflags & (MNT_MS_LOOP |
MNT_MS_OFFSET |
MNT_MS_SIZELIMIT)) {
DBG(LOOP, ul_debugobj(cxt, "loopdev specific options detected"));
return 1;
}
if ((cxt->mountflags & (MS_BIND | MS_MOVE))
|| mnt_context_propagation_only(cxt))
return 0;
/* Automatically create a loop device from a regular file if a
* filesystem is not specified or the filesystem is known for libblkid
* (these filesystems work with block devices only). The file size
* should be at least 1KiB, otherwise we will create an empty loopdev with
* no mountable filesystem...
*
* Note that there is no restriction (on kernel side) that would prevent a regular
* file as a mount(2) source argument. A filesystem that is able to mount
* regular files could be implemented.
*/
type = mnt_fs_get_fstype(cxt->fs);
if (mnt_fs_is_regular(cxt->fs) &&
(!type || strcmp(type, "auto") == 0 || blkid_known_fstype(type))) {
struct stat st;
if (stat(src, &st) == 0 && S_ISREG(st.st_mode) &&
st.st_size > 1024) {
DBG(LOOP, ul_debugobj(cxt, "automatically enabling loop= option"));
cxt->user_mountflags |= MNT_MS_LOOP;
mnt_optstr_append_option(&cxt->fs->user_optstr, "loop", NULL);
return 1;
}
}
return 0;
}
/* Check if there already exists a mounted loop device on the mountpoint node
* with the same parameters.
*/
static int __attribute__((nonnull))
is_mounted_same_loopfile(struct libmnt_context *cxt,
const char *target,
const char *backing_file,
uint64_t offset)
{
struct libmnt_table *tb;
struct libmnt_iter itr;
struct libmnt_fs *fs;
struct libmnt_cache *cache;
const char *bf;
int rc = 0;
struct libmnt_ns *ns_old;
assert(cxt);
assert(cxt->fs);
assert((cxt->flags & MNT_FL_MOUNTFLAGS_MERGED));
if (mnt_context_get_mtab(cxt, &tb))
return 0;
ns_old = mnt_context_switch_target_ns(cxt);
if (!ns_old)
return -MNT_ERR_NAMESPACE;
DBG(LOOP, ul_debugobj(cxt, "checking if %s mounted on %s",
backing_file, target));
cache = mnt_context_get_cache(cxt);
mnt_reset_iter(&itr, MNT_ITER_BACKWARD);
bf = cache ? mnt_resolve_path(backing_file, cache) : backing_file;
/* Search for a mountpoint node in mtab, proceed if any of these have the
* loop option set or the device is a loop device
*/
while (rc == 0 && mnt_table_next_fs(tb, &itr, &fs) == 0) {
const char *src = mnt_fs_get_source(fs);
const char *opts = mnt_fs_get_user_options(fs);
char *val;
size_t len;
if (!src || !mnt_fs_match_target(fs, target, cache))
continue;
rc = 0;
if (strncmp(src, "/dev/loop", 9) == 0) {
rc = loopdev_is_used((char *) src, bf, offset, 0, LOOPDEV_FL_OFFSET);
} else if (opts && (cxt->user_mountflags & MNT_MS_LOOP) &&
mnt_optstr_get_option(opts, "loop", &val, &len) == 0 && val) {
val = strndup(val, len);
rc = loopdev_is_used((char *) val, bf, offset, 0, LOOPDEV_FL_OFFSET);
free(val);
}
}
if (rc)
DBG(LOOP, ul_debugobj(cxt, "%s already mounted", backing_file));
if (!mnt_context_switch_ns(cxt, ns_old))
return -MNT_ERR_NAMESPACE;
return rc;
}
int mnt_context_setup_loopdev(struct libmnt_context *cxt)
{
const char *backing_file, *optstr, *loopdev = NULL;
char *val = NULL, *loopval = NULL;
size_t len;
struct loopdev_cxt lc;
int rc = 0, lo_flags = 0;
uint64_t offset = 0, sizelimit = 0;
bool reuse = FALSE;
assert(cxt);
assert(cxt->fs);
assert((cxt->flags & MNT_FL_MOUNTFLAGS_MERGED));
backing_file = mnt_fs_get_srcpath(cxt->fs);
if (!backing_file)
return -EINVAL;
DBG(LOOP, ul_debugobj(cxt, "trying to setup device for %s", backing_file));
if (cxt->mountflags & MS_RDONLY) {
DBG(LOOP, ul_debugobj(cxt, "enabling READ-ONLY flag"));
lo_flags |= LO_FLAGS_READ_ONLY;
}
optstr = mnt_fs_get_user_options(cxt->fs);
/*
* loop=
*/
if (rc == 0 && (cxt->user_mountflags & MNT_MS_LOOP) &&
mnt_optstr_get_option(optstr, "loop", &val, &len) == 0 && val) {
loopval = strndup(val, len);
rc = loopval ? 0 : -ENOMEM;
}
/*
* offset=
*/
if (rc == 0 && (cxt->user_mountflags & MNT_MS_OFFSET) &&
mnt_optstr_get_option(optstr, "offset", &val, &len) == 0) {
rc = mnt_parse_offset(val, len, &offset);
if (rc) {
DBG(LOOP, ul_debugobj(cxt, "failed to parse offset="));
rc = -MNT_ERR_MOUNTOPT;
}
}
/*
* sizelimit=
*/
if (rc == 0 && (cxt->user_mountflags & MNT_MS_SIZELIMIT) &&
mnt_optstr_get_option(optstr, "sizelimit", &val, &len) == 0) {
rc = mnt_parse_offset(val, len, &sizelimit);
if (rc) {
DBG(LOOP, ul_debugobj(cxt, "failed to parse sizelimit="));
rc = -MNT_ERR_MOUNTOPT;
}
}
/*
* encryption=
*/
if (rc == 0 && (cxt->user_mountflags & MNT_MS_ENCRYPTION) &&
mnt_optstr_get_option(optstr, "encryption", &val, &len) == 0) {
DBG(LOOP, ul_debugobj(cxt, "encryption no longer supported"));
rc = -MNT_ERR_MOUNTOPT;
}
if (rc == 0 && is_mounted_same_loopfile(cxt,
mnt_context_get_target(cxt),
backing_file, offset))
rc = -EBUSY;
if (rc)
goto done_no_deinit;
/* It is possible to mount the same file more times. If we set more
* than one loop device referring to the same file, kernel has no
* mechanism to detect it. To prevent data corruption, the same loop
* device has to be recycled.
*/
if (backing_file) {
rc = loopcxt_init(&lc, 0);
if (rc)
goto done_no_deinit;
rc = loopcxt_find_overlap(&lc, backing_file, offset, sizelimit);
switch (rc) {
case 0: /* not found */
DBG(LOOP, ul_debugobj(cxt, "not found overlapping loopdev"));
loopcxt_deinit(&lc);
break;
case 1: /* overlap */
DBG(LOOP, ul_debugobj(cxt, "overlapping %s detected",
loopcxt_get_device(&lc)));
rc = -MNT_ERR_LOOPOVERLAP;
goto done;
case 2: /* overlap -- full size and offset match (reuse) */
{
uint32_t lc_encrypt_type;
DBG(LOOP, ul_debugobj(cxt, "re-using existing loop device %s",
loopcxt_get_device(&lc)));
/* Once a loop is initialized RO, there is no
* way to change its parameters. */
if (loopcxt_is_readonly(&lc)
&& !(lo_flags & LO_FLAGS_READ_ONLY)) {
DBG(LOOP, ul_debugobj(cxt, "%s is read-only",
loopcxt_get_device(&lc)));
rc = -EROFS;
goto done;
}
/* This is no more supported, but check to be safe. */
if (loopcxt_get_encrypt_type(&lc, &lc_encrypt_type) == 0
&& lc_encrypt_type != LO_CRYPT_NONE) {
DBG(LOOP, ul_debugobj(cxt, "encryption no longer supported for device %s",
loopcxt_get_device(&lc)));
rc = -MNT_ERR_LOOPOVERLAP;
goto done;
}
rc = 0;
/* loop= used with argument. Conflict will occur. */
if (loopval) {
rc = -MNT_ERR_LOOPOVERLAP;
goto done;
} else {
reuse = TRUE;
goto success;
}
}
default: /* error */
goto done;
}
}
DBG(LOOP, ul_debugobj(cxt, "not found; create a new loop device"));
rc = loopcxt_init(&lc, 0);
if (rc)
goto done_no_deinit;
if (loopval) {
rc = loopcxt_set_device(&lc, loopval);
if (rc == 0)
loopdev = loopcxt_get_device(&lc);
}
if (rc)
goto done;
/* since 2.6.37 we don't have to store backing filename to mtab
* because kernel provides the name in /sys.
*/
if (get_linux_version() >= KERNEL_VERSION(2, 6, 37) ||
!mnt_context_mtab_writable(cxt)) {
DBG(LOOP, ul_debugobj(cxt, "enabling AUTOCLEAR flag"));
lo_flags |= LO_FLAGS_AUTOCLEAR;
}
do {
/* found free device */
if (!loopdev) {
rc = loopcxt_find_unused(&lc);
if (rc)
goto done;
DBG(LOOP, ul_debugobj(cxt, "trying to use %s",
loopcxt_get_device(&lc)));
}
/* set device attributes
* -- note that loopcxt_find_unused() resets "lc"
*/
rc = loopcxt_set_backing_file(&lc, backing_file);
if (!rc && offset)
rc = loopcxt_set_offset(&lc, offset);
if (!rc && sizelimit)
rc = loopcxt_set_sizelimit(&lc, sizelimit);
if (!rc)
loopcxt_set_flags(&lc, lo_flags);
if (rc) {
DBG(LOOP, ul_debugobj(cxt, "failed to set loop attributes"));
goto done;
}
/* setup the device */
rc = loopcxt_setup_device(&lc);
if (!rc)
break; /* success */
if (loopdev || rc != -EBUSY) {
DBG(LOOP, ul_debugobj(cxt, "failed to setup device"));
rc = -MNT_ERR_LOOPDEV;
goto done;
}
DBG(LOOP, ul_debugobj(cxt, "device stolen...trying again"));
} while (1);
success:
if (!rc)
rc = mnt_fs_set_source(cxt->fs, loopcxt_get_device(&lc));
if (!rc) {
/* success */
cxt->flags |= MNT_FL_LOOPDEV_READY;
if (reuse || ( (cxt->user_mountflags & MNT_MS_LOOP) &&
loopcxt_is_autoclear(&lc))) {
/*
* autoclear flag accepted by the kernel, don't store
* the "loop=" option to mtab.
*/
DBG(LOOP, ul_debugobj(cxt, "removing unnecessary loop= from mtab"));
cxt->user_mountflags &= ~MNT_MS_LOOP;
mnt_optstr_remove_option(&cxt->fs->user_optstr, "loop");
}
if (!(cxt->mountflags & MS_RDONLY) &&
loopcxt_is_readonly(&lc))
/*
* mount planned read-write, but loopdev is read-only,
* let's fix mount options...
*/
mnt_context_set_mflags(cxt, cxt->mountflags | MS_RDONLY);
/* we have to keep the device open until mount(1),
* otherwise it will be auto-cleared by kernel
*/
cxt->loopdev_fd = loopcxt_get_fd(&lc);
if (cxt->loopdev_fd < 0) {
DBG(LOOP, ul_debugobj(cxt, "failed to get loopdev FD"));
rc = -errno;
} else
loopcxt_set_fd(&lc, -1, 0);
}
done:
loopcxt_deinit(&lc);
done_no_deinit:
free(loopval);
return rc;
}
/*
* Deletes loop device
*/
int mnt_context_delete_loopdev(struct libmnt_context *cxt)
{
const char *src;
int rc;
assert(cxt);
assert(cxt->fs);
src = mnt_fs_get_srcpath(cxt->fs);
if (!src)
return -EINVAL;
if (cxt->loopdev_fd > -1)
close(cxt->loopdev_fd);
rc = loopdev_delete(src);
cxt->flags &= ~MNT_FL_LOOPDEV_READY;
cxt->loopdev_fd = -1;
DBG(LOOP, ul_debugobj(cxt, "deleted [rc=%d]", rc));
return rc;
}
/*
* Clears loopdev stuff in context, should be called after
* failed or successful mount(2).
*/
int mnt_context_clear_loopdev(struct libmnt_context *cxt)
{
assert(cxt);
if (mnt_context_get_status(cxt) == 0 &&
(cxt->flags & MNT_FL_LOOPDEV_READY)) {
/*
* mount(2) failed, delete loopdev
*/
mnt_context_delete_loopdev(cxt);
} else if (cxt->loopdev_fd > -1) {
/*
* mount(2) success, close the device
*/
DBG(LOOP, ul_debugobj(cxt, "closing FD"));
close(cxt->loopdev_fd);
}
cxt->loopdev_fd = -1;
return 0;
}
