Patch "loop: fix concurrent lo_open/lo_release" has been added to the 4.4-stable tree

Patch "loop: fix concurrent lo_open/lo_release" has been added to the 4.4-stable tree

[gregkh]

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;a=summary

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