loop: fix concurrent lo_open/lo_release (ae665016) · Commits · 戴 / test

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:

范龙飞 <long7573@126.com> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by:

Jens Axboe <axboe@kernel.dk>

drivers/block/loop.c

+8 −2

Original line number	Diff line number	Diff line
		@@ -1581,9 +1581,8 @@ out:
		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,

Admin message