4.20-stable review patch. If anyone has any objections, please let me know.
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From: Tetsuo Handa penguin-kernel@I-love.SAKURA.ne.jp
commit 310ca162d779efee8a2dc3731439680f3e9c1e86 upstream.
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=f3cfe26e785d85f9ee259f385515291d21bd80a... [2] https://syzkaller.appspot.com/bug?id=bf154052f0eea4bc7712499e4569505907d1588...
Signed-off-by: Tetsuo Handa penguin-kernel@I-love.SAKURA.ne.jp Reported-by: syzbot syzbot+bf89c128e05dd6c62523@syzkaller.appspotmail.com Reviewed-by: Jan Kara jack@suse.cz Signed-off-by: Jan Kara jack@suse.cz Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/block/loop.c | 58 +++++++++++++++++++++++++-------------------------- drivers/block/loop.h | 1 2 files changed, 29 insertions(+), 30 deletions(-)
--- 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_devic */ 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_devic 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, 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, 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 * 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 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 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 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 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 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 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_devic 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_
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_dev 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_dev 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 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 * 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 fi 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; --- 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;