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Commit ae665016 authored by Linus Torvalds's avatar Linus Torvalds Committed by Jens Axboe
Browse files

loop: fix concurrent lo_open/lo_release 



范龙飞 reports that KASAN can report a use-after-free in __lock_acquire.
The reason is due to insufficient serialization in lo_release(), which
will continue to use the loop device even after it has decremented the
lo_refcnt to zero.

In the meantime, another process can come in, open the loop device
again as it is being shut down. Confusion ensues.

Reported-by: default avatar范龙飞 <long7573@126.com>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent cbf3a959

drivers/block/loop.c

+8 −2
Original line number Diff line number Diff line
@@ -1581,9 +1581,8 @@ static int lo_open(struct block_device *bdev, fmode_t mode) 
	return err;

}



static void lo_release(struct gendisk *disk, fmode_t mode)

static void __lo_release(struct loop_device *lo)

{

	struct loop_device *lo = disk->private_data;

	int err;



	if (atomic_dec_return(&lo->lo_refcnt))
@@ -1610,6 +1609,13 @@ static void lo_release(struct gendisk *disk, fmode_t mode) 
	mutex_unlock(&lo->lo_ctl_mutex);

}



static void lo_release(struct gendisk *disk, fmode_t mode)

{

	mutex_lock(&loop_index_mutex);

	__lo_release(disk->private_data);

	mutex_unlock(&loop_index_mutex);

}



static const struct block_device_operations lo_fops = {

	.owner =	THIS_MODULE,

	.open =		lo_open,