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block/loop: Use global lock for ioctl() operation.
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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 <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>
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Tetsuo Handa authored and Jens Axboe committed Nov 8, 2018
1 parent b1ab5fa commit 310ca16
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Showing 2 changed files with 29 additions and 30 deletions.
58 changes: 29 additions & 29 deletions drivers/block/loop.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand Down Expand Up @@ -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;
}

Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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;
}

Expand All @@ -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);
Expand Down Expand Up @@ -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);
Expand All @@ -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);
Expand Down Expand Up @@ -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;

Expand All @@ -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;
Expand All @@ -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;
Expand All @@ -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;
Expand All @@ -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;
Expand Down Expand Up @@ -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);
Expand All @@ -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:
Expand Down Expand Up @@ -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
Expand All @@ -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)
Expand Down Expand Up @@ -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;
}

Expand Down Expand Up @@ -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);
Expand Down Expand Up @@ -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;
Expand Down
1 change: 0 additions & 1 deletion drivers/block/loop.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand Down

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