[v3,6/6] loop: be paranoid on exit and prevent new additions / removals
diff mbox series

Message ID 20200429074627.5955-7-mcgrof@kernel.org
State New
Headers show
Series
  • block: fix blktrace debugfs use after free
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Commit Message

Luis Chamberlain April 29, 2020, 7:46 a.m. UTC
Be pedantic on removal as well and hold the mutex.
This should prevent uses of addition while we exit.

Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
---
 drivers/block/loop.c | 4 ++++
 1 file changed, 4 insertions(+)

Comments

Greg KH April 29, 2020, 9:50 a.m. UTC | #1
On Wed, Apr 29, 2020 at 07:46:27AM +0000, Luis Chamberlain wrote:
> Be pedantic on removal as well and hold the mutex.
> This should prevent uses of addition while we exit.
> 
> Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
> ---
>  drivers/block/loop.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index da693e6a834e..6dccba22c9b5 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -2333,6 +2333,8 @@ static void __exit loop_exit(void)
>  
>  	range = max_loop ? max_loop << part_shift : 1UL << MINORBITS;
>  
> +	mutex_lock(&loop_ctl_mutex);
> +
>  	idr_for_each(&loop_index_idr, &loop_exit_cb, NULL);
>  	idr_destroy(&loop_index_idr);
>  
> @@ -2340,6 +2342,8 @@ static void __exit loop_exit(void)
>  	unregister_blkdev(LOOP_MAJOR, "loop");
>  
>  	misc_deregister(&loop_misc);
> +
> +	mutex_unlock(&loop_ctl_mutex);
>  }
>  
>  module_init(loop_init);

What type of issue is this helping with?  Can it be triggered today?  if
so, shouldn't it be backported to stable kernels?

thanks,

greg k-h
Ming Lei April 29, 2020, 2:05 p.m. UTC | #2
On Wed, Apr 29, 2020 at 07:46:27AM +0000, Luis Chamberlain wrote:
> Be pedantic on removal as well and hold the mutex.
> This should prevent uses of addition while we exit.
> 
> Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
> ---
>  drivers/block/loop.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index da693e6a834e..6dccba22c9b5 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -2333,6 +2333,8 @@ static void __exit loop_exit(void)
>  
>  	range = max_loop ? max_loop << part_shift : 1UL << MINORBITS;
>  
> +	mutex_lock(&loop_ctl_mutex);
> +
>  	idr_for_each(&loop_index_idr, &loop_exit_cb, NULL);
>  	idr_destroy(&loop_index_idr);
>  
> @@ -2340,6 +2342,8 @@ static void __exit loop_exit(void)
>  	unregister_blkdev(LOOP_MAJOR, "loop");
>  
>  	misc_deregister(&loop_misc);
> +
> +	mutex_unlock(&loop_ctl_mutex);
>  }
>  
>  module_init(loop_init);
> -- 
> 2.25.1
> 

Reviewed-by: Ming Lei <ming.lei@redhat.com>
Luis Chamberlain May 3, 2020, 9:09 a.m. UTC | #3
On Wed, Apr 29, 2020 at 11:50:34AM +0200, Greg KH wrote:
> On Wed, Apr 29, 2020 at 07:46:27AM +0000, Luis Chamberlain wrote:
> > Be pedantic on removal as well and hold the mutex.
> > This should prevent uses of addition while we exit.
> > 
> > Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
> > ---
> >  drivers/block/loop.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> > index da693e6a834e..6dccba22c9b5 100644
> > --- a/drivers/block/loop.c
> > +++ b/drivers/block/loop.c
> > @@ -2333,6 +2333,8 @@ static void __exit loop_exit(void)
> >  
> >  	range = max_loop ? max_loop << part_shift : 1UL << MINORBITS;
> >  
> > +	mutex_lock(&loop_ctl_mutex);
> > +
> >  	idr_for_each(&loop_index_idr, &loop_exit_cb, NULL);
> >  	idr_destroy(&loop_index_idr);
> >  
> > @@ -2340,6 +2342,8 @@ static void __exit loop_exit(void)
> >  	unregister_blkdev(LOOP_MAJOR, "loop");
> >  
> >  	misc_deregister(&loop_misc);
> > +
> > +	mutex_unlock(&loop_ctl_mutex);
> >  }
> >  
> >  module_init(loop_init);
> 
> What type of issue is this helping with?  Can it be triggered today?  if
> so, shouldn't it be backported to stable kernels?

Just code inspection. I can't trigger a userspace test script to crash
the kernel yet, but suspect a race still does exist.

  Luis

Patch
diff mbox series

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index da693e6a834e..6dccba22c9b5 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -2333,6 +2333,8 @@  static void __exit loop_exit(void)
 
 	range = max_loop ? max_loop << part_shift : 1UL << MINORBITS;
 
+	mutex_lock(&loop_ctl_mutex);
+
 	idr_for_each(&loop_index_idr, &loop_exit_cb, NULL);
 	idr_destroy(&loop_index_idr);
 
@@ -2340,6 +2342,8 @@  static void __exit loop_exit(void)
 	unregister_blkdev(LOOP_MAJOR, "loop");
 
 	misc_deregister(&loop_misc);
+
+	mutex_unlock(&loop_ctl_mutex);
 }
 
 module_init(loop_init);