[t,x,z,a,b,1/1] loop: fix concurrent lo_open/lo_release

Message ID 20180131164800.20056-2-benjamin.romer@canonical.com
State New
Headers show
Series
  • Fix for CVE-2018-5344
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Commit Message

Benjamin M Romer Jan. 31, 2018, 4:48 p.m.
From: Linus Torvalds <torvalds@linux-foundation.org>

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>

CVE-2018-5344
(cherry picked from commit ae6650163c66a7eff1acd6eb8b0f752dcfa8eba5)
Signed-off-by: Benjamin M Romer <benjamin.romer@canonical.com>
---
 drivers/block/loop.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

Patch

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 7cfc35ef879f..5e643357dbe4 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1624,9 +1624,8 @@  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))
@@ -1652,6 +1651,13 @@  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,