[trusty,1/1] loop: fix concurrent lo_open/lo_release

Message ID 20180131164759.20006-2-benjamin.romer@canonical.com
State New
Headers show
Series
  • Fix for CVE-2018-5344
Related show

Commit Message

Benjamin M Romer Jan. 31, 2018, 4:47 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)
[ ben_r: patch needed to be fuzzed to apply. ]
Signed-off-by: Benjamin M Romer <benjamin.romer@canonical.com>
---
 drivers/block/loop.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

Comments

Stefan Bader Feb. 28, 2018, 9:54 a.m. | #1
On 31.01.2018 17:47, Benjamin M Romer wrote:
> 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)
> [ ben_r: patch needed to be fuzzed to apply. ]
> Signed-off-by: Benjamin M Romer <benjamin.romer@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.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 2e229ac..abcb856 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -1529,9 +1529,8 @@ 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;
>  
>  	mutex_lock(&lo->lo_ctl_mutex);
> @@ -1559,6 +1558,13 @@ out:
>  	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,
>

Patch

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 2e229ac..abcb856 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1529,9 +1529,8 @@  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;
 
 	mutex_lock(&lo->lo_ctl_mutex);
@@ -1559,6 +1558,13 @@  out:
 	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,