syzbot is reporting circular locking dependency between bdev->bd_mutex and lo->lo_ctl_mutex [1] which is caused by calling blkdev_reread_part() with lock held. We need to drop lo->lo_ctl_mutex in order to fix it.
This patch fixes it by combining loop_index_mutex and loop_ctl_mutex into loop_mutex, and releasing loop_mutex before calling blkdev_reread_part() or fput() or path_put() or leaving ioctl(). The rule is that current thread calls lock_loop() before accessing "struct loop_device", and current thread no longer accesses "struct loop_device" after unlock_loop() is called. Since syzbot is reporting various bugs [2] where a race in the loop module is suspected, let's check whether this patch affects these bugs too. [1] https://syzkaller.appspot.com/bug?id=bf154052f0eea4bc7712499e4569505907d15889 [2] https://syzkaller.appspot.com/bug?id=b3c7e1440aa8ece16bf557dbac427fdff1dad9d6 Signed-off-by: Tetsuo Handa <penguin-ker...@i-love.sakura.ne.jp> Reported-by: syzbot <syzbot+4684a000d5abdade83fac55b1e7d1f935ef19...@syzkaller.appspotmail.com> --- drivers/block/loop.c | 187 ++++++++++++++++++++++++++++----------------------- 1 file changed, 101 insertions(+), 86 deletions(-) diff --git a/drivers/block/loop.c b/drivers/block/loop.c index 4b05a27..04389bb 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -84,12 +84,50 @@ #include <linux/uaccess.h> static DEFINE_IDR(loop_index_idr); -static DEFINE_MUTEX(loop_index_mutex); -static DEFINE_MUTEX(loop_ctl_mutex); +static DEFINE_MUTEX(loop_mutex); +static void *loop_mutex_owner; /* == __mutex_owner(&loop_mutex) */ static int max_part; static int part_shift; +/* + * lock_loop - Lock loop_mutex. + */ +static void lock_loop(void) +{ + mutex_lock(&loop_mutex); + loop_mutex_owner = current; +} + +/* + * lock_loop_killable - Lock loop_mutex unless killed. + */ +static int lock_loop_killable(void) +{ + int err = mutex_lock_killable(&loop_mutex); + + if (err) + return err; + loop_mutex_owner = current; + return 0; +} + +/* + * unlock_loop - Unlock loop_mutex as needed. + * + * Explicitly call this function before calling fput() or blkdev_reread_part() + * in order to avoid circular lock dependency. After this function is called, + * current thread is no longer allowed to access "struct loop_device" memory, + * for another thread would access that memory as soon as loop_mutex is held. + */ +static void unlock_loop(void) +{ + if (loop_mutex_owner == current) { + loop_mutex_owner = NULL; + mutex_unlock(&loop_mutex); + } +} + static int transfer_xor(struct loop_device *lo, int cmd, struct page *raw_page, unsigned raw_off, struct page *loop_page, unsigned loop_off, @@ -637,6 +675,7 @@ static void loop_reread_partitions(struct loop_device *lo, const int count = atomic_read(&lo->lo_refcnt); memcpy(filename, lo->lo_file_name, sizeof(filename)); + unlock_loop(); /* * bd_mutex has been held already in release path, so don't @@ -699,6 +738,7 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev, struct file *file, *old_file; int error; + lockdep_assert_held(&loop_mutex); error = -ENXIO; if (lo->lo_state != Lo_bound) goto out; @@ -737,10 +777,12 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev, if (lo->lo_flags & LO_FLAGS_PARTSCAN) loop_reread_partitions(lo, bdev); + unlock_loop(); fput(old_file); return 0; out_putf: + unlock_loop(); fput(file); out: return error; @@ -918,6 +960,7 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode, int error; loff_t size; + lockdep_assert_held(&loop_mutex); /* This is safe, since we have a reference from open(). */ __module_get(THIS_MODULE); @@ -991,6 +1034,7 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode, return 0; out_putf: + unlock_loop(); fput(file); out: /* This is safe: open() is still holding a reference. */ @@ -1042,6 +1086,7 @@ static int loop_clr_fd(struct loop_device *lo) struct block_device *bdev = lo->lo_device; bool reread; + lockdep_assert_held(&loop_mutex); if (lo->lo_state != Lo_bound) return -ENXIO; @@ -1057,7 +1102,6 @@ static int loop_clr_fd(struct loop_device *lo) */ if (atomic_read(&lo->lo_refcnt) > 1) { lo->lo_flags |= LO_FLAGS_AUTOCLEAR; - mutex_unlock(&loop_ctl_mutex); return 0; } @@ -1111,13 +1155,7 @@ static int loop_clr_fd(struct loop_device *lo) lo->lo_disk->flags |= GENHD_FL_NO_PART_SCAN; if (reread) loop_reread_partitions(lo, bdev); - mutex_unlock(&loop_ctl_mutex); - /* - * Need not hold loop_ctl_mutex to fput backing file. - * Calling fput holding loop_ctl_mutex triggers a circular - * lock dependency possibility warning as fput can take - * bd_mutex which is usually taken before loop_ctl_mutex. - */ + unlock_loop(); fput(filp); return 0; } @@ -1129,6 +1167,7 @@ static int loop_clr_fd(struct loop_device *lo) struct loop_func_table *xfer; kuid_t uid = current_uid(); + lockdep_assert_held(&loop_mutex); if (lo->lo_encrypt_key_size && !uid_eq(lo->lo_key_owner, uid) && !capable(CAP_SYS_ADMIN)) @@ -1220,10 +1259,9 @@ static int loop_clr_fd(struct loop_device *lo) struct kstat stat; int ret; - if (lo->lo_state != Lo_bound) { - mutex_unlock(&loop_ctl_mutex); + lockdep_assert_held(&loop_mutex); + if (lo->lo_state != Lo_bound) return -ENXIO; - } memset(info, 0, sizeof(*info)); info->lo_number = lo->lo_number; @@ -1240,10 +1278,10 @@ static int loop_clr_fd(struct loop_device *lo) lo->lo_encrypt_key_size); } - /* Drop loop_ctl_mutex while we call into the filesystem. */ + /* Drop loop_mutex while we call into the filesystem. */ path = lo->lo_backing_file->f_path; path_get(&path); - mutex_unlock(&loop_ctl_mutex); + unlock_loop(); ret = vfs_getattr(&path, &stat, STATX_INO, AT_STATX_SYNC_AS_STAT); if (!ret) { info->lo_device = huge_encode_dev(stat.dev); @@ -1334,10 +1372,8 @@ static int loop_clr_fd(struct loop_device *lo) struct loop_info64 info64; int err; - if (!arg) { - mutex_unlock(&loop_ctl_mutex); + if (!arg) return -EINVAL; - } err = loop_get_status(lo, &info64); if (!err) err = loop_info64_to_old(&info64, &info); @@ -1352,10 +1388,8 @@ static int loop_clr_fd(struct loop_device *lo) struct loop_info64 info64; int err; - if (!arg) { - mutex_unlock(&loop_ctl_mutex); + if (!arg) return -EINVAL; - } err = loop_get_status(lo, &info64); if (!err && copy_to_user(arg, &info64, sizeof(info64))) err = -EFAULT; @@ -1365,6 +1399,7 @@ static int loop_clr_fd(struct loop_device *lo) static int loop_set_capacity(struct loop_device *lo) { + lockdep_assert_held(&loop_mutex); if (unlikely(lo->lo_state != Lo_bound)) return -ENXIO; @@ -1374,6 +1409,8 @@ static int loop_set_capacity(struct loop_device *lo) static int loop_set_dio(struct loop_device *lo, unsigned long arg) { int error = -ENXIO; + + lockdep_assert_held(&loop_mutex); if (lo->lo_state != Lo_bound) goto out; @@ -1387,6 +1424,7 @@ static int loop_set_dio(struct loop_device *lo, unsigned long arg) static int loop_set_block_size(struct loop_device *lo, unsigned long arg) { + lockdep_assert_held(&loop_mutex); if (lo->lo_state != Lo_bound) return -ENXIO; @@ -1409,11 +1447,10 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode, unsigned int cmd, unsigned long arg) { struct loop_device *lo = bdev->bd_disk->private_data; - int err; + int err = lock_loop_killable(); - err = mutex_lock_killable_nested(&loop_ctl_mutex, 1); if (err) - goto out_unlocked; + return err; switch (cmd) { case LOOP_SET_FD: @@ -1423,10 +1460,7 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode, err = loop_change_fd(lo, bdev, arg); break; case LOOP_CLR_FD: - /* loop_clr_fd would have unlocked loop_ctl_mutex on success */ err = loop_clr_fd(lo); - if (!err) - goto out_unlocked; break; case LOOP_SET_STATUS: err = -EPERM; @@ -1436,8 +1470,7 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode, break; case LOOP_GET_STATUS: err = loop_get_status_old(lo, (struct loop_info __user *) arg); - /* loop_get_status() unlocks loop_ctl_mutex */ - goto out_unlocked; + break; case LOOP_SET_STATUS64: err = -EPERM; if ((mode & FMODE_WRITE) || capable(CAP_SYS_ADMIN)) @@ -1446,8 +1479,7 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode, break; case LOOP_GET_STATUS64: err = loop_get_status64(lo, (struct loop_info64 __user *) arg); - /* loop_get_status() unlocks loop_ctl_mutex */ - goto out_unlocked; + break; case LOOP_SET_CAPACITY: err = -EPERM; if ((mode & FMODE_WRITE) || capable(CAP_SYS_ADMIN)) @@ -1466,9 +1498,7 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode, default: err = lo->ioctl ? lo->ioctl(lo, cmd, arg) : -EINVAL; } - mutex_unlock(&loop_ctl_mutex); - -out_unlocked: + unlock_loop(); return err; } @@ -1582,10 +1612,8 @@ struct compat_loop_info { struct loop_info64 info64; int err; - if (!arg) { - mutex_unlock(&loop_ctl_mutex); + if (!arg) return -EINVAL; - } err = loop_get_status(lo, &info64); if (!err) err = loop_info64_to_compat(&info64, arg); @@ -1600,20 +1628,16 @@ static int lo_compat_ioctl(struct block_device *bdev, fmode_t mode, switch(cmd) { case LOOP_SET_STATUS: - err = mutex_lock_killable(&loop_ctl_mutex); - if (!err) { + err = lock_loop_killable(); + if (!err) err = loop_set_status_compat(lo, (const struct compat_loop_info __user *)arg); - mutex_unlock(&loop_ctl_mutex); - } break; case LOOP_GET_STATUS: - err = mutex_lock_killable(&loop_ctl_mutex); - if (!err) { + err = lock_loop_killable(); + if (!err) err = loop_get_status_compat(lo, (struct compat_loop_info __user *)arg); - /* loop_get_status() unlocks loop_ctl_mutex */ - } break; case LOOP_SET_CAPACITY: case LOOP_CLR_FD: @@ -1630,6 +1654,7 @@ static int lo_compat_ioctl(struct block_device *bdev, fmode_t mode, err = -ENOIOCTLCMD; break; } + unlock_loop(); return err; } #endif @@ -1637,37 +1662,31 @@ static int lo_compat_ioctl(struct block_device *bdev, fmode_t mode, static int lo_open(struct block_device *bdev, fmode_t mode) { struct loop_device *lo; - int err = 0; + int err = lock_loop_killable(); - mutex_lock(&loop_index_mutex); + if (err) + return err; lo = bdev->bd_disk->private_data; - if (!lo) { + if (!lo) err = -ENXIO; - goto out; - } - - atomic_inc(&lo->lo_refcnt); -out: - mutex_unlock(&loop_index_mutex); + else + atomic_inc(&lo->lo_refcnt); + unlock_loop(); return err; } static void __lo_release(struct loop_device *lo) { - int err; - if (atomic_dec_return(&lo->lo_refcnt)) return; - mutex_lock(&loop_ctl_mutex); + lockdep_assert_held(&loop_mutex); if (lo->lo_flags & LO_FLAGS_AUTOCLEAR) { /* * In autoclear mode, stop the loop thread * and remove configuration after last close. */ - err = loop_clr_fd(lo); - if (!err) - return; + loop_clr_fd(lo); } else if (lo->lo_state == Lo_bound) { /* * Otherwise keep thread (if running) and config, @@ -1676,15 +1695,13 @@ static void __lo_release(struct loop_device *lo) blk_mq_freeze_queue(lo->lo_queue); blk_mq_unfreeze_queue(lo->lo_queue); } - - mutex_unlock(&loop_ctl_mutex); } static void lo_release(struct gendisk *disk, fmode_t mode) { - mutex_lock(&loop_index_mutex); + lock_loop(); __lo_release(disk->private_data); - mutex_unlock(&loop_index_mutex); + unlock_loop(); } static const struct block_device_operations lo_fops = { @@ -1723,10 +1740,8 @@ static int unregister_transfer_cb(int id, void *ptr, void *data) struct loop_device *lo = ptr; struct loop_func_table *xfer = data; - mutex_lock(&loop_ctl_mutex); if (lo->lo_encryption == xfer) loop_release_xfer(lo); - mutex_unlock(&loop_ctl_mutex); return 0; } @@ -1738,8 +1753,14 @@ int loop_unregister_transfer(int number) if (n == 0 || n >= MAX_LO_CRYPT || (xfer = xfer_funcs[n]) == NULL) return -EINVAL; + /* + * cleanup_cryptoloop() cannot handle errors because it is called + * from module_exit(). Thus, don't give up upon SIGKILL here. + */ + lock_loop(); xfer_funcs[n] = NULL; idr_for_each(&loop_index_idr, &unregister_transfer_cb, xfer); + unlock_loop(); return 0; } @@ -1982,20 +2003,18 @@ static int loop_lookup(struct loop_device **l, int i) static struct kobject *loop_probe(dev_t dev, int *part, void *data) { struct loop_device *lo; - struct kobject *kobj; - int err; + struct kobject *kobj = NULL; + int err = lock_loop_killable(); - mutex_lock(&loop_index_mutex); + *part = 0; + if (err) + return NULL; err = loop_lookup(&lo, MINOR(dev) >> part_shift); if (err < 0) err = loop_add(&lo, MINOR(dev) >> part_shift); - if (err < 0) - kobj = NULL; - else + if (err >= 0) kobj = get_disk_and_module(lo->lo_disk); - mutex_unlock(&loop_index_mutex); - - *part = 0; + unlock_loop(); return kobj; } @@ -2003,9 +2022,11 @@ static long loop_control_ioctl(struct file *file, unsigned int cmd, unsigned long parm) { struct loop_device *lo; - int ret = -ENOSYS; + int ret = lock_loop_killable(); - mutex_lock(&loop_index_mutex); + if (ret) + return ret; + ret = -ENOSYS; switch (cmd) { case LOOP_CTL_ADD: ret = loop_lookup(&lo, parm); @@ -2019,21 +2040,15 @@ static long loop_control_ioctl(struct file *file, unsigned int cmd, ret = loop_lookup(&lo, parm); if (ret < 0) break; - ret = mutex_lock_killable(&loop_ctl_mutex); - if (ret) - break; if (lo->lo_state != Lo_unbound) { ret = -EBUSY; - mutex_unlock(&loop_ctl_mutex); break; } if (atomic_read(&lo->lo_refcnt) > 0) { ret = -EBUSY; - mutex_unlock(&loop_ctl_mutex); break; } lo->lo_disk->private_data = NULL; - mutex_unlock(&loop_ctl_mutex); idr_remove(&loop_index_idr, lo->lo_number); loop_remove(lo); break; @@ -2043,7 +2058,7 @@ static long loop_control_ioctl(struct file *file, unsigned int cmd, break; ret = loop_add(&lo, -1); } - mutex_unlock(&loop_index_mutex); + unlock_loop(); return ret; } @@ -2127,10 +2142,10 @@ static int __init loop_init(void) THIS_MODULE, loop_probe, NULL, NULL); /* pre-create number of devices given by config or max_loop */ - mutex_lock(&loop_index_mutex); + lock_loop(); for (i = 0; i < nr; i++) loop_add(&lo, i); - mutex_unlock(&loop_index_mutex); + unlock_loop(); printk(KERN_INFO "loop: module loaded\n"); return 0; -- 1.8.3.1
