APPLIED[T]: [SRU][Trusty][PATCH 1/1] loop: fix concurrent lo_open/lo_release

[Stefan Bader]

On 29.01.2018 17:16, Kleber Sacilotto de Souza wrote:
> From: Linus Torvalds <torvalds at linux-foundation.org>
> 
> CVE-2018-5344
> 
> 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 at 126.com>
> Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
> Signed-off-by: Jens Axboe <axboe at kernel.dk>
> (backported from commit ae6650163c66a7eff1acd6eb8b0f752dcfa8eba5 upstream)
> Signed-off-by: Kleber Sacilotto de Souza <kleber.souza at 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 2e229ac94bdb..abcb85688916 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,
> 


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