/* SPDX-License-Identifier: LGPL-2.1-or-later */ #if HAVE_VALGRIND_MEMCHECK_H #include #endif #include #include #include #include #include #include #include #include #include "sd-device.h" #include "alloc-util.h" #include "blockdev-util.h" #include "device-util.h" #include "errno-util.h" #include "fd-util.h" #include "fileio.h" #include "loop-util.h" #include "missing_loop.h" #include "parse-util.h" #include "random-util.h" #include "stat-util.h" #include "stdio-util.h" #include "string-util.h" #include "tmpfile-util.h" static void cleanup_clear_loop_close(int *fd) { if (*fd < 0) return; (void) ioctl(*fd, LOOP_CLR_FD); (void) safe_close(*fd); } static int loop_is_bound(int fd) { struct loop_info64 info; assert(fd >= 0); if (ioctl(fd, LOOP_GET_STATUS64, &info) < 0) { if (errno == ENXIO) return false; /* not bound! */ return -errno; } return true; /* bound! */ } static int get_current_uevent_seqnum(uint64_t *ret) { _cleanup_free_ char *p = NULL; int r; r = read_full_virtual_file("/sys/kernel/uevent_seqnum", &p, NULL); if (r < 0) return log_debug_errno(r, "Failed to read current uevent sequence number: %m"); truncate_nl(p); r = safe_atou64(p, ret); if (r < 0) return log_debug_errno(r, "Failed to parse current uevent sequence number: %s", p); return 0; } static int device_has_block_children(sd_device *d) { _cleanup_(sd_device_enumerator_unrefp) sd_device_enumerator *e = NULL; const char *main_sn, *main_ss; sd_device *q; int r; assert(d); /* Checks if the specified device currently has block device children (i.e. partition block * devices). */ r = sd_device_get_sysname(d, &main_sn); if (r < 0) return r; r = sd_device_get_subsystem(d, &main_ss); if (r < 0) return r; if (!streq(main_ss, "block")) return -EINVAL; r = sd_device_enumerator_new(&e); if (r < 0) return r; r = sd_device_enumerator_allow_uninitialized(e); if (r < 0) return r; r = sd_device_enumerator_add_match_parent(e, d); if (r < 0) return r; FOREACH_DEVICE(e, q) { const char *ss, *sn; r = sd_device_get_subsystem(q, &ss); if (r < 0) continue; if (!streq(ss, "block")) continue; r = sd_device_get_sysname(q, &sn); if (r < 0) continue; if (streq(sn, main_sn)) continue; return 1; /* we have block device children */ } return 0; } static int loop_configure( int fd, int nr, const struct loop_config *c, bool *try_loop_configure, uint64_t *ret_seqnum_not_before) { _cleanup_(sd_device_unrefp) sd_device *d = NULL; _cleanup_free_ char *sysname = NULL; _cleanup_close_ int lock_fd = -1; uint64_t seqnum; int r; assert(fd >= 0); assert(nr >= 0); assert(c); assert(try_loop_configure); if (asprintf(&sysname, "loop%i", nr) < 0) return -ENOMEM; r = sd_device_new_from_subsystem_sysname(&d, "block", sysname); if (r < 0) return r; /* Let's lock the device before we do anything. We take the BSD lock on a second, separately opened * fd for the device. udev after all watches for close() events (specifically IN_CLOSE_WRITE) on * block devices to reprobe them, hence by having a separate fd we will later close() we can ensure * we trigger udev after everything is done. If we'd lock our own fd instead and keep it open for a * long time udev would possibly never run on it again, even though the fd is unlocked, simply * because we never close() it. It also has the nice benefit we can use the _cleanup_close_ logic to * automatically release the lock, after we are done. */ lock_fd = fd_reopen(fd, O_RDWR|O_CLOEXEC|O_NONBLOCK|O_NOCTTY); if (lock_fd < 0) return lock_fd; if (flock(lock_fd, LOCK_EX) < 0) return -errno; /* Let's see if the device is really detached, i.e. currently has no associated partition block * devices. On various kernels (such as 5.8) it is possible to have a loopback block device that * superficially is detached but still has partition block devices associated for it. They only go * away when the device is reattached. (Yes, LOOP_CLR_FD doesn't work then, because officially * nothing is attached and LOOP_CTL_REMOVE doesn't either, since it doesn't care about partition * block devices. */ r = device_has_block_children(d); if (r < 0) return r; if (r > 0) { r = loop_is_bound(fd); if (r < 0) return r; if (r > 0) return -EBUSY; return -EUCLEAN; /* Bound but children? Tell caller to reattach something so that the * partition block devices are gone too. */ } if (*try_loop_configure) { /* Acquire uevent seqnum immediately before attaching the loopback device. This allows * callers to ignore all uevents with a seqnum before this one, if they need to associate * uevent with this attachment. Doing so isn't race-free though, as uevents that happen in * the window between this reading of the seqnum, and the LOOP_CONFIGURE call might still be * mistaken as originating from our attachment, even though might be caused by an earlier * use. But doing this at least shortens the race window a bit. */ r = get_current_uevent_seqnum(&seqnum); if (r < 0) return r; if (ioctl(fd, LOOP_CONFIGURE, c) < 0) { /* Do fallback only if LOOP_CONFIGURE is not supported, propagate all other * errors. Note that the kernel is weird: non-existing ioctls currently return EINVAL * rather than ENOTTY on loopback block devices. They should fix that in the kernel, * but in the meantime we accept both here. */ if (!ERRNO_IS_NOT_SUPPORTED(errno) && errno != EINVAL) return -errno; *try_loop_configure = false; } else { bool good = true; if (c->info.lo_sizelimit != 0) { /* Kernel 5.8 vanilla doesn't properly propagate the size limit into the * block device. If it's used, let's immediately check if it had the desired * effect hence. And if not use classic LOOP_SET_STATUS64. */ uint64_t z; if (ioctl(fd, BLKGETSIZE64, &z) < 0) { r = -errno; goto fail; } if (z != c->info.lo_sizelimit) { log_debug("LOOP_CONFIGURE is broken, doesn't honour .lo_sizelimit. Falling back to LOOP_SET_STATUS64."); good = false; } } if (FLAGS_SET(c->info.lo_flags, LO_FLAGS_PARTSCAN)) { /* Kernel 5.8 vanilla doesn't properly propagate the partition scanning flag * into the block device. Let's hence verify if things work correctly here * before returning. */ r = blockdev_partscan_enabled(fd); if (r < 0) goto fail; if (r == 0) { log_debug("LOOP_CONFIGURE is broken, doesn't honour LO_FLAGS_PARTSCAN. Falling back to LOOP_SET_STATUS64."); good = false; } } if (!good) { /* LOOP_CONFIGURE doesn't work. Remember that. */ *try_loop_configure = false; /* We return EBUSY here instead of retrying immediately with LOOP_SET_FD, * because LOOP_CLR_FD is async: if the operation cannot be executed right * away it just sets the autoclear flag on the device. This means there's a * good chance we cannot actually reuse the loopback device right-away. Hence * let's assume it's busy, avoid the trouble and let the calling loop call us * again with a new, likely unused device. */ r = -EBUSY; goto fail; } if (ret_seqnum_not_before) *ret_seqnum_not_before = seqnum; return 0; } } /* Let's read the seqnum again, to shorten the window. */ r = get_current_uevent_seqnum(&seqnum); if (r < 0) return r; /* Since kernel commit 5db470e229e22b7eda6e23b5566e532c96fb5bc3 (kernel v5.0) the LOOP_SET_STATUS64 * ioctl can return EAGAIN in case we change the lo_offset field, if someone else is accessing the * block device while we try to reconfigure it. This is a pretty common case, since udev might * instantly start probing the device as soon as we attach an fd to it. Hence handle it in two ways: * first, let's take the BSD lock to ensure that udev will not step in between the point in * time where we attach the fd and where we reconfigure the device. Secondly, let's wait 50ms on * EAGAIN and retry. The former should be an efficient mechanism to avoid we have to wait 50ms * needlessly if we are just racing against udev. The latter is protection against all other cases, * i.e. peers that do not take the BSD lock. */ if (ioctl(fd, LOOP_SET_FD, c->fd) < 0) return -errno; for (unsigned n_attempts = 0;;) { if (ioctl(fd, LOOP_SET_STATUS64, &c->info) >= 0) break; if (errno != EAGAIN || ++n_attempts >= 64) { r = log_debug_errno(errno, "Failed to configure loopback device: %m"); goto fail; } /* Sleep some random time, but at least 10ms, at most 250ms. Increase the delay the more * failed attempts we see */ (void) usleep(UINT64_C(10) * USEC_PER_MSEC + random_u64_range(UINT64_C(240) * USEC_PER_MSEC * n_attempts/64)); } if (ret_seqnum_not_before) *ret_seqnum_not_before = seqnum; return 0; fail: (void) ioctl(fd, LOOP_CLR_FD); return r; } static int attach_empty_file(int loop, int nr) { _cleanup_close_ int fd = -1; /* So here's the thing: on various kernels (5.8 at least) loop block devices might enter a state * where they are detached but nonetheless have partitions, when used heavily. Accessing these * partitions results in immediatey IO errors. There's no pretty way to get rid of them * again. Neither LOOP_CLR_FD nor LOOP_CTL_REMOVE suffice (see above). What does work is to * reassociate them with a new fd however. This is what we do here hence: we associate the devices * with an empty file (i.e. an image that definitely has no partitions). We then immediately clear it * again. This suffices to make the partitions go away. Ugly but appears to work. */ log_debug("Found unattached loopback block device /dev/loop%i with partitions. Attaching empty file to remove them.", nr); fd = open_tmpfile_unlinkable(NULL, O_RDONLY); if (fd < 0) return fd; if (flock(loop, LOCK_EX) < 0) return -errno; if (ioctl(loop, LOOP_SET_FD, fd) < 0) return -errno; if (ioctl(loop, LOOP_SET_STATUS64, &(struct loop_info64) { .lo_flags = LO_FLAGS_READ_ONLY| LO_FLAGS_AUTOCLEAR| LO_FLAGS_PARTSCAN, /* enable partscan, so that the partitions really go away */ }) < 0) return -errno; if (ioctl(loop, LOOP_CLR_FD) < 0) return -errno; /* The caller is expected to immediately close the loopback device after this, so that the BSD lock * is released, and udev sees the changes. */ return 0; } int loop_device_make( int fd, int open_flags, uint64_t offset, uint64_t size, uint32_t loop_flags, LoopDevice **ret) { _cleanup_free_ char *loopdev = NULL; bool try_loop_configure = true; struct loop_config config; LoopDevice *d = NULL; uint64_t seqnum = UINT64_MAX; struct stat st; int nr = -1, r; assert(fd >= 0); assert(ret); assert(IN_SET(open_flags, O_RDWR, O_RDONLY)); if (fstat(fd, &st) < 0) return -errno; if (S_ISBLK(st.st_mode)) { if (ioctl(fd, LOOP_GET_STATUS64, &config.info) >= 0) { /* Oh! This is a loopback device? That's interesting! */ #if HAVE_VALGRIND_MEMCHECK_H /* Valgrind currently doesn't know LOOP_GET_STATUS64. Remove this once it does */ VALGRIND_MAKE_MEM_DEFINED(&config.info, sizeof(config.info)); #endif nr = config.info.lo_number; if (asprintf(&loopdev, "/dev/loop%i", nr) < 0) return -ENOMEM; } if (offset == 0 && IN_SET(size, 0, UINT64_MAX)) { _cleanup_close_ int copy = -1; /* If this is already a block device, store a copy of the fd as it is */ copy = fcntl(fd, F_DUPFD_CLOEXEC, 3); if (copy < 0) return -errno; d = new(LoopDevice, 1); if (!d) return -ENOMEM; *d = (LoopDevice) { .fd = TAKE_FD(copy), .nr = nr, .node = TAKE_PTR(loopdev), .relinquished = true, /* It's not allocated by us, don't destroy it when this object is freed */ .devno = st.st_rdev, .uevent_seqnum_not_before = UINT64_MAX, }; *ret = d; return d->fd; } } else { r = stat_verify_regular(&st); if (r < 0) return r; } _cleanup_close_ int control = -1; _cleanup_(cleanup_clear_loop_close) int loop_with_fd = -1; control = open("/dev/loop-control", O_RDWR|O_CLOEXEC|O_NOCTTY|O_NONBLOCK); if (control < 0) return -errno; config = (struct loop_config) { .fd = fd, .info = { /* Use the specified flags, but configure the read-only flag from the open flags, and force autoclear */ .lo_flags = (loop_flags & ~LO_FLAGS_READ_ONLY) | ((open_flags & O_ACCMODE) == O_RDONLY ? LO_FLAGS_READ_ONLY : 0) | LO_FLAGS_AUTOCLEAR, .lo_offset = offset, .lo_sizelimit = size == UINT64_MAX ? 0 : size, }, }; /* Loop around LOOP_CTL_GET_FREE, since at the moment we attempt to open the returned device it might * be gone already, taken by somebody else racing against us. */ for (unsigned n_attempts = 0;;) { _cleanup_close_ int loop = -1; nr = ioctl(control, LOOP_CTL_GET_FREE); if (nr < 0) return -errno; if (asprintf(&loopdev, "/dev/loop%i", nr) < 0) return -ENOMEM; loop = open(loopdev, O_CLOEXEC|O_NONBLOCK|O_NOCTTY|open_flags); if (loop < 0) { /* Somebody might've gotten the same number from the kernel, used the device, * and called LOOP_CTL_REMOVE on it. Let's retry with a new number. */ if (!IN_SET(errno, ENOENT, ENXIO)) return -errno; } else { r = loop_configure(loop, nr, &config, &try_loop_configure, &seqnum); if (r >= 0) { loop_with_fd = TAKE_FD(loop); break; } if (r == -EUCLEAN) { /* Make left-over partition disappear hack (see above) */ r = attach_empty_file(loop, nr); if (r < 0 && r != -EBUSY) return r; } else if (r != -EBUSY) return r; } if (++n_attempts >= 64) /* Give up eventually */ return -EBUSY; loopdev = mfree(loopdev); /* Wait some random time, to make collision less likely. Let's pick a random time in the * range 0ms…250ms, linearly scaled by the number of failed attempts. */ (void) usleep(random_u64_range(UINT64_C(10) * USEC_PER_MSEC + UINT64_C(240) * USEC_PER_MSEC * n_attempts/64)); } if (fstat(loop_with_fd, &st) < 0) return -errno; assert(S_ISBLK(st.st_mode)); d = new(LoopDevice, 1); if (!d) return -ENOMEM; *d = (LoopDevice) { .fd = TAKE_FD(loop_with_fd), .node = TAKE_PTR(loopdev), .nr = nr, .devno = st.st_rdev, .uevent_seqnum_not_before = seqnum, }; *ret = d; return d->fd; } int loop_device_make_by_path( const char *path, int open_flags, uint32_t loop_flags, LoopDevice **ret) { _cleanup_close_ int fd = -1; int r; assert(path); assert(ret); assert(open_flags < 0 || IN_SET(open_flags, O_RDWR, O_RDONLY)); /* Passing < 0 as open_flags here means we'll try to open the device writable if we can, retrying * read-only if we cannot. */ fd = open(path, O_CLOEXEC|O_NONBLOCK|O_NOCTTY|(open_flags >= 0 ? open_flags : O_RDWR)); if (fd < 0) { r = -errno; /* Retry read-only? */ if (open_flags >= 0 || !(ERRNO_IS_PRIVILEGE(r) || r == -EROFS)) return r; fd = open(path, O_CLOEXEC|O_NONBLOCK|O_NOCTTY|O_RDONLY); if (fd < 0) return r; /* Propagate original error */ open_flags = O_RDONLY; } else if (open_flags < 0) open_flags = O_RDWR; return loop_device_make(fd, open_flags, 0, 0, loop_flags, ret); } LoopDevice* loop_device_unref(LoopDevice *d) { if (!d) return NULL; if (d->fd >= 0) { /* Implicitly sync the device, since otherwise in-flight blocks might not get written */ if (fsync(d->fd) < 0) log_debug_errno(errno, "Failed to sync loop block device, ignoring: %m"); if (d->nr >= 0 && !d->relinquished) { if (ioctl(d->fd, LOOP_CLR_FD) < 0) log_debug_errno(errno, "Failed to clear loop device: %m"); } safe_close(d->fd); } if (d->nr >= 0 && !d->relinquished) { _cleanup_close_ int control = -1; control = open("/dev/loop-control", O_RDWR|O_CLOEXEC|O_NOCTTY|O_NONBLOCK); if (control < 0) log_warning_errno(errno, "Failed to open loop control device, cannot remove loop device %s: %m", strna(d->node)); else for (unsigned n_attempts = 0;;) { if (ioctl(control, LOOP_CTL_REMOVE, d->nr) >= 0) break; if (errno != EBUSY || ++n_attempts >= 64) { log_warning_errno(errno, "Failed to remove device %s: %m", strna(d->node)); break; } (void) usleep(50 * USEC_PER_MSEC); } } free(d->node); return mfree(d); } void loop_device_relinquish(LoopDevice *d) { assert(d); /* Don't attempt to clean up the loop device anymore from this point on. Leave the clean-ing up to the kernel * itself, using the loop device "auto-clear" logic we already turned on when creating the device. */ d->relinquished = true; } int loop_device_open(const char *loop_path, int open_flags, LoopDevice **ret) { _cleanup_close_ int loop_fd = -1; _cleanup_free_ char *p = NULL; struct loop_info64 info; struct stat st; LoopDevice *d; int nr; assert(loop_path); assert(ret); loop_fd = open(loop_path, O_CLOEXEC|O_NONBLOCK|O_NOCTTY|open_flags); if (loop_fd < 0) return -errno; if (fstat(loop_fd, &st) < 0) return -errno; if (!S_ISBLK(st.st_mode)) return -ENOTBLK; if (ioctl(loop_fd, LOOP_GET_STATUS64, &info) >= 0) { #if HAVE_VALGRIND_MEMCHECK_H /* Valgrind currently doesn't know LOOP_GET_STATUS64. Remove this once it does */ VALGRIND_MAKE_MEM_DEFINED(&info, sizeof(info)); #endif nr = info.lo_number; } else nr = -1; p = strdup(loop_path); if (!p) return -ENOMEM; d = new(LoopDevice, 1); if (!d) return -ENOMEM; *d = (LoopDevice) { .fd = TAKE_FD(loop_fd), .nr = nr, .node = TAKE_PTR(p), .relinquished = true, /* It's not ours, don't try to destroy it when this object is freed */ .devno = st.st_dev, .uevent_seqnum_not_before = UINT64_MAX, }; *ret = d; return d->fd; } static int resize_partition(int partition_fd, uint64_t offset, uint64_t size) { char sysfs[STRLEN("/sys/dev/block/:/partition") + 2*DECIMAL_STR_MAX(dev_t) + 1]; _cleanup_free_ char *whole = NULL, *buffer = NULL; uint64_t current_offset, current_size, partno; _cleanup_close_ int whole_fd = -1; struct stat st; dev_t devno; int r; assert(partition_fd >= 0); /* Resizes the partition the loopback device refer to (assuming it refers to one instead of an actual * loopback device), and changes the offset, if needed. This is a fancy wrapper around * BLKPG_RESIZE_PARTITION. */ if (fstat(partition_fd, &st) < 0) return -errno; assert(S_ISBLK(st.st_mode)); xsprintf(sysfs, "/sys/dev/block/%u:%u/partition", major(st.st_rdev), minor(st.st_rdev)); r = read_one_line_file(sysfs, &buffer); if (r == -ENOENT) /* not a partition, cannot resize */ return -ENOTTY; if (r < 0) return r; r = safe_atou64(buffer, &partno); if (r < 0) return r; xsprintf(sysfs, "/sys/dev/block/%u:%u/start", major(st.st_rdev), minor(st.st_rdev)); buffer = mfree(buffer); r = read_one_line_file(sysfs, &buffer); if (r < 0) return r; r = safe_atou64(buffer, ¤t_offset); if (r < 0) return r; if (current_offset > UINT64_MAX/512U) return -EINVAL; current_offset *= 512U; if (ioctl(partition_fd, BLKGETSIZE64, ¤t_size) < 0) return -EINVAL; if (size == UINT64_MAX && offset == UINT64_MAX) return 0; if (current_size == size && current_offset == offset) return 0; xsprintf(sysfs, "/sys/dev/block/%u:%u/../dev", major(st.st_rdev), minor(st.st_rdev)); buffer = mfree(buffer); r = read_one_line_file(sysfs, &buffer); if (r < 0) return r; r = parse_dev(buffer, &devno); if (r < 0) return r; r = device_path_make_major_minor(S_IFBLK, devno, &whole); if (r < 0) return r; whole_fd = open(whole, O_RDWR|O_CLOEXEC|O_NONBLOCK|O_NOCTTY); if (whole_fd < 0) return -errno; struct blkpg_partition bp = { .pno = partno, .start = offset == UINT64_MAX ? current_offset : offset, .length = size == UINT64_MAX ? current_size : size, }; struct blkpg_ioctl_arg ba = { .op = BLKPG_RESIZE_PARTITION, .data = &bp, .datalen = sizeof(bp), }; if (ioctl(whole_fd, BLKPG, &ba) < 0) return -errno; return 0; } int loop_device_refresh_size(LoopDevice *d, uint64_t offset, uint64_t size) { struct loop_info64 info; assert(d); /* Changes the offset/start of the loop device relative to the beginning of the underlying file or * block device. If this loop device actually refers to a partition and not a loopback device, we'll * try to adjust the partition offsets instead. * * If either offset or size is UINT64_MAX we won't change that parameter. */ if (d->fd < 0) return -EBADF; if (d->nr < 0) /* not a loopback device */ return resize_partition(d->fd, offset, size); if (ioctl(d->fd, LOOP_GET_STATUS64, &info) < 0) return -errno; #if HAVE_VALGRIND_MEMCHECK_H /* Valgrind currently doesn't know LOOP_GET_STATUS64. Remove this once it does */ VALGRIND_MAKE_MEM_DEFINED(&info, sizeof(info)); #endif if (size == UINT64_MAX && offset == UINT64_MAX) return 0; if (info.lo_sizelimit == size && info.lo_offset == offset) return 0; if (size != UINT64_MAX) info.lo_sizelimit = size; if (offset != UINT64_MAX) info.lo_offset = offset; if (ioctl(d->fd, LOOP_SET_STATUS64, &info) < 0) return -errno; return 0; } int loop_device_flock(LoopDevice *d, int operation) { assert(d); if (d->fd < 0) return -EBADF; if (flock(d->fd, operation) < 0) return -errno; return 0; } int loop_device_sync(LoopDevice *d) { assert(d); /* We also do this implicitly in loop_device_unref(). Doing this explicitly here has the benefit that * we can check the return value though. */ if (d->fd < 0) return -EBADF; if (fsync(d->fd) < 0) return -errno; return 0; }