diff options
Diffstat (limited to 'libmount/src/context_loopdev.c')
| -rw-r--r-- | libmount/src/context_loopdev.c | 465 |
1 files changed, 465 insertions, 0 deletions
diff --git a/libmount/src/context_loopdev.c b/libmount/src/context_loopdev.c new file mode 100644 index 0000000..62e319c --- /dev/null +++ b/libmount/src/context_loopdev.c @@ -0,0 +1,465 @@ +/* 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_regularfs(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 = 0; + + DBG(LOOP, ul_debugobj(cxt, "re-using existing loop device %s", + loopcxt_get_device(&lc))); + + /* Open loop device to block device autoclear... */ + if (loopcxt_get_fd(&lc) < 0) { + DBG(LOOP, ul_debugobj(cxt, "failed to get loopdev FD")); + rc = -errno; + goto done; + } + + /* + * Now that we certainly have the loop device open, + * verify the loop device was not autocleared in the + * mean time. + */ + if (!loopcxt_get_info(&lc)) { + DBG(LOOP, ul_debugobj(cxt, "lost race with %s teardown", + loopcxt_get_device(&lc))); + loopcxt_deinit(&lc); + break; + } + + /* 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; +} + |