Re: kernel NULL pointer dereference in gntdev_mmap -> mmu_interval_notifier_remove

[Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>]

On Mon, Apr 19, 2021 at 11:33:27AM +0200, Juergen Gross wrote:
> Could you try the attached patch?

I've tried and it works, as in - I didn't get the crash in ~20 runs.
Since the issue is quite hard to reproduce, I'm not fully sure it
helped, but sounds plausible. I think you can treat this as Tested-by:
;)

Thanks!

> From 7ff3c32b36279aacef9cf80f4103fc6050759c10 Mon Sep 17 00:00:00 2001
> From: Juergen Gross <jgross@xxxxxxxx>
> Date: Mon, 19 Apr 2021 11:15:59 +0200
> Subject: [PATCH] xen/gntdev: fix gntdev_mmap() error exit path
> MIME-Version: 1.0
> Content-Type: text/plain; charset=UTF-8
> Content-Transfer-Encoding: 8bit
> 
> Commit d3eeb1d77c5d0af ("xen/gntdev: use mmu_interval_notifier_insert")
> introduced an error in gntdev_mmap(): in case the call of
> mmu_interval_notifier_insert_locked() fails the exit path should not
> call mmu_interval_notifier_remove().
> 
> One reason for failure is e.g. a signal pending for the running
> process.
> 
> Fixes: d3eeb1d77c5d0af ("xen/gntdev: use mmu_interval_notifier_insert")
> Cc: stable@xxxxxxxxxxxxxxx
> Reported-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> ---
>  drivers/xen/gntdev.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
> index f01d58c7a042..a3e7be96527d 100644
> --- a/drivers/xen/gntdev.c
> +++ b/drivers/xen/gntdev.c
> @@ -1017,8 +1017,10 @@ static int gntdev_mmap(struct file *flip, struct 
> vm_area_struct *vma)
>               err = mmu_interval_notifier_insert_locked(
>                       &map->notifier, vma->vm_mm, vma->vm_start,
>                       vma->vm_end - vma->vm_start, &gntdev_mmu_ops);
> -             if (err)
> +             if (err) {
> +                     map->vma = NULL;
>                       goto out_unlock_put;
> +             }
>       }
>       mutex_unlock(&priv->lock);
>  






-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab

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