From 310ca162d779efee8a2dc3731439680f3e9c1e86 Mon Sep 17 00:00:00 2001 From: Tetsuo Handa Date: Thu, 8 Nov 2018 14:01:02 +0100 Subject: [PATCH] block/loop: Use global lock for ioctl() operation. syzbot is reporting NULL pointer dereference [1] which is caused by race condition between ioctl(loop_fd, LOOP_CLR_FD, 0) versus ioctl(other_loop_fd, LOOP_SET_FD, loop_fd) due to traversing other loop devices at loop_validate_file() without holding corresponding lo->lo_ctl_mutex locks. Since ioctl() request on loop devices is not frequent operation, we don't need fine grained locking. Let's use global lock in order to allow safe traversal at loop_validate_file(). Note that syzbot is also reporting circular locking dependency between bdev->bd_mutex and lo->lo_ctl_mutex [2] which is caused by calling blkdev_reread_part() with lock held. This patch does not address it. [1] https://syzkaller.appspot.com/bug?id=f3cfe26e785d85f9ee259f385515291d21bd80a3 [2] https://syzkaller.appspot.com/bug?id=bf154052f0eea4bc7712499e4569505907d15889 Signed-off-by: Tetsuo Handa Reported-by: syzbot Reviewed-by: Jan Kara Signed-off-by: Jan Kara Signed-off-by: Jens Axboe --- drivers/block/loop.c | 58 ++++++++++++++++++++++---------------------- drivers/block/loop.h | 1 - 2 files changed, 29 insertions(+), 30 deletions(-) diff --git a/drivers/block/loop.c b/drivers/block/loop.c index a29ef169f360..63008e879771 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -84,6 +84,7 @@ static DEFINE_IDR(loop_index_idr); static DEFINE_MUTEX(loop_index_mutex); +static DEFINE_MUTEX(loop_ctl_mutex); static int max_part; static int part_shift; @@ -1046,7 +1047,7 @@ static int loop_clr_fd(struct loop_device *lo) */ if (atomic_read(&lo->lo_refcnt) > 1) { lo->lo_flags |= LO_FLAGS_AUTOCLEAR; - mutex_unlock(&lo->lo_ctl_mutex); + mutex_unlock(&loop_ctl_mutex); return 0; } @@ -1099,12 +1100,12 @@ static int loop_clr_fd(struct loop_device *lo) if (!part_shift) lo->lo_disk->flags |= GENHD_FL_NO_PART_SCAN; loop_unprepare_queue(lo); - mutex_unlock(&lo->lo_ctl_mutex); + mutex_unlock(&loop_ctl_mutex); /* - * Need not hold lo_ctl_mutex to fput backing file. - * Calling fput holding lo_ctl_mutex triggers a circular + * 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 lo_ctl_mutex. + * bd_mutex which is usually taken before loop_ctl_mutex. */ fput(filp); return 0; @@ -1209,7 +1210,7 @@ loop_get_status(struct loop_device *lo, struct loop_info64 *info) int ret; if (lo->lo_state != Lo_bound) { - mutex_unlock(&lo->lo_ctl_mutex); + mutex_unlock(&loop_ctl_mutex); return -ENXIO; } @@ -1228,10 +1229,10 @@ loop_get_status(struct loop_device *lo, struct loop_info64 *info) lo->lo_encrypt_key_size); } - /* Drop lo_ctl_mutex while we call into the filesystem. */ + /* Drop loop_ctl_mutex while we call into the filesystem. */ path = lo->lo_backing_file->f_path; path_get(&path); - mutex_unlock(&lo->lo_ctl_mutex); + mutex_unlock(&loop_ctl_mutex); ret = vfs_getattr(&path, &stat, STATX_INO, AT_STATX_SYNC_AS_STAT); if (!ret) { info->lo_device = huge_encode_dev(stat.dev); @@ -1323,7 +1324,7 @@ loop_get_status_old(struct loop_device *lo, struct loop_info __user *arg) { int err; if (!arg) { - mutex_unlock(&lo->lo_ctl_mutex); + mutex_unlock(&loop_ctl_mutex); return -EINVAL; } err = loop_get_status(lo, &info64); @@ -1341,7 +1342,7 @@ loop_get_status64(struct loop_device *lo, struct loop_info64 __user *arg) { int err; if (!arg) { - mutex_unlock(&lo->lo_ctl_mutex); + mutex_unlock(&loop_ctl_mutex); return -EINVAL; } err = loop_get_status(lo, &info64); @@ -1399,7 +1400,7 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode, struct loop_device *lo = bdev->bd_disk->private_data; int err; - err = mutex_lock_killable_nested(&lo->lo_ctl_mutex, 1); + err = mutex_lock_killable_nested(&loop_ctl_mutex, 1); if (err) goto out_unlocked; @@ -1411,7 +1412,7 @@ 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 lo_ctl_mutex on success */ + /* loop_clr_fd would have unlocked loop_ctl_mutex on success */ err = loop_clr_fd(lo); if (!err) goto out_unlocked; @@ -1424,7 +1425,7 @@ 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 lo_ctl_mutex */ + /* loop_get_status() unlocks loop_ctl_mutex */ goto out_unlocked; case LOOP_SET_STATUS64: err = -EPERM; @@ -1434,7 +1435,7 @@ 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 lo_ctl_mutex */ + /* loop_get_status() unlocks loop_ctl_mutex */ goto out_unlocked; case LOOP_SET_CAPACITY: err = -EPERM; @@ -1454,7 +1455,7 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode, default: err = lo->ioctl ? lo->ioctl(lo, cmd, arg) : -EINVAL; } - mutex_unlock(&lo->lo_ctl_mutex); + mutex_unlock(&loop_ctl_mutex); out_unlocked: return err; @@ -1571,7 +1572,7 @@ loop_get_status_compat(struct loop_device *lo, int err; if (!arg) { - mutex_unlock(&lo->lo_ctl_mutex); + mutex_unlock(&loop_ctl_mutex); return -EINVAL; } err = loop_get_status(lo, &info64); @@ -1588,19 +1589,19 @@ static int lo_compat_ioctl(struct block_device *bdev, fmode_t mode, switch(cmd) { case LOOP_SET_STATUS: - err = mutex_lock_killable(&lo->lo_ctl_mutex); + err = mutex_lock_killable(&loop_ctl_mutex); if (!err) { err = loop_set_status_compat(lo, (const struct compat_loop_info __user *)arg); - mutex_unlock(&lo->lo_ctl_mutex); + mutex_unlock(&loop_ctl_mutex); } break; case LOOP_GET_STATUS: - err = mutex_lock_killable(&lo->lo_ctl_mutex); + err = mutex_lock_killable(&loop_ctl_mutex); if (!err) { err = loop_get_status_compat(lo, (struct compat_loop_info __user *)arg); - /* loop_get_status() unlocks lo_ctl_mutex */ + /* loop_get_status() unlocks loop_ctl_mutex */ } break; case LOOP_SET_CAPACITY: @@ -1647,7 +1648,7 @@ static void __lo_release(struct loop_device *lo) if (atomic_dec_return(&lo->lo_refcnt)) return; - mutex_lock(&lo->lo_ctl_mutex); + mutex_lock(&loop_ctl_mutex); if (lo->lo_flags & LO_FLAGS_AUTOCLEAR) { /* * In autoclear mode, stop the loop thread @@ -1665,7 +1666,7 @@ static void __lo_release(struct loop_device *lo) blk_mq_unfreeze_queue(lo->lo_queue); } - mutex_unlock(&lo->lo_ctl_mutex); + mutex_unlock(&loop_ctl_mutex); } static void lo_release(struct gendisk *disk, fmode_t mode) @@ -1711,10 +1712,10 @@ static int unregister_transfer_cb(int id, void *ptr, void *data) struct loop_device *lo = ptr; struct loop_func_table *xfer = data; - mutex_lock(&lo->lo_ctl_mutex); + mutex_lock(&loop_ctl_mutex); if (lo->lo_encryption == xfer) loop_release_xfer(lo); - mutex_unlock(&lo->lo_ctl_mutex); + mutex_unlock(&loop_ctl_mutex); return 0; } @@ -1895,7 +1896,6 @@ static int loop_add(struct loop_device **l, int i) if (!part_shift) disk->flags |= GENHD_FL_NO_PART_SCAN; disk->flags |= GENHD_FL_EXT_DEVT; - mutex_init(&lo->lo_ctl_mutex); atomic_set(&lo->lo_refcnt, 0); lo->lo_number = i; spin_lock_init(&lo->lo_lock); @@ -2008,21 +2008,21 @@ static long loop_control_ioctl(struct file *file, unsigned int cmd, ret = loop_lookup(&lo, parm); if (ret < 0) break; - ret = mutex_lock_killable(&lo->lo_ctl_mutex); + ret = mutex_lock_killable(&loop_ctl_mutex); if (ret) break; if (lo->lo_state != Lo_unbound) { ret = -EBUSY; - mutex_unlock(&lo->lo_ctl_mutex); + mutex_unlock(&loop_ctl_mutex); break; } if (atomic_read(&lo->lo_refcnt) > 0) { ret = -EBUSY; - mutex_unlock(&lo->lo_ctl_mutex); + mutex_unlock(&loop_ctl_mutex); break; } lo->lo_disk->private_data = NULL; - mutex_unlock(&lo->lo_ctl_mutex); + mutex_unlock(&loop_ctl_mutex); idr_remove(&loop_index_idr, lo->lo_number); loop_remove(lo); break; diff --git a/drivers/block/loop.h b/drivers/block/loop.h index 4d42c7af7de7..af75a5ee4094 100644 --- a/drivers/block/loop.h +++ b/drivers/block/loop.h @@ -54,7 +54,6 @@ struct loop_device { spinlock_t lo_lock; int lo_state; - struct mutex lo_ctl_mutex; struct kthread_worker worker; struct task_struct *worker_task; bool use_dio;