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From d5e06a1867210049bbfe27864ee0a40cfd9b1e9b Mon Sep 17 00:00:00 2001
From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Fri, 5 Jan 2018 16:26:00 -0800
Subject: [PATCH] loop: fix concurrent lo_open/lo_release
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
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.
CVE: CVE-2018-5344
Upstream-Status: Backport [https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=linux-4.14.y&id=d5e06a1867210049bbfe27864ee0a40cfd9b1e9b]
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>
Signed-off-by: Andreas Wellving <andreas.wellving@enea.com>
---
drivers/block/loop.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 85de67334695..a2a0dce5114e 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1576,9 +1576,8 @@ 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))
@@ -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,
--
2.20.1
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