This is a note to let you know that I've just added the patch titled

loop: fix concurrent lo_open/lo_release

to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: loop-fix-concurrent-lo_open-lo_release.patch and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From ae6650163c66a7eff1acd6eb8b0f752dcfa8eba5 Mon Sep 17 00:00:00 2001

From: Linus Torvalds torvalds@linux-foundation.org Date: Fri, 5 Jan 2018 16:26:00 -0800 Subject: loop: fix concurrent lo_open/lo_release MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit

From: Linus Torvalds torvalds@linux-foundation.org

commit ae6650163c66a7eff1acd6eb8b0f752dcfa8eba5 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

--- drivers/block/loop.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-)

--- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -1569,9 +1569,8 @@ 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)) @@ -1597,6 +1596,13 @@ static void lo_release(struct gendisk *d 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,

Patches currently in stable-queue which might be from torvalds@linux-foundation.org are

queue-4.4/loop-fix-concurrent-lo_open-lo_release.patch