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loop: fix concurrent lo_open/lo_release 

commit ae6650163c upstream.

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>
Cc: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
pull/10/head
Linus Torvalds 2018-01-05 16:26:00 -08:00 committed by Greg Kroah-Hartman
parent d383a4277b
commit d5e06a1867
1 changed files with 8 additions and 2 deletions
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10
drivers/block/loop.c
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@ -1576,9 +1576,8 @@ 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))
@ -1605,6 +1604,13 @@ 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,