Subject: Re: [PATCH v2] Uprobes: Fix kernel oops with delayed_uprobe_remove()

From: Srikar Dronamraju <[email-masked]>
Date: Wed, 5 Dec 2018 15:31:41 +0530

* Ravi Bangoria <[email-masked]> [2018-12-05 09:04:23]:

> There could be a race between task exit and probe unregister:
> 
>   exit_mm()
>   mmput()
>   __mmput()                     uprobe_unregister()
>   uprobe_clear_state()          put_uprobe()
>   delayed_uprobe_remove()       delayed_uprobe_remove()
> 
> put_uprobe() is calling delayed_uprobe_remove() without taking
> delayed_uprobe_lock and thus the race sometimes results in a
> kernel crash. Fix this by taking delayed_uprobe_lock before
> calling delayed_uprobe_remove() from put_uprobe().
> 
> Detailed crash log can be found at:
>   https://lkml.org/lkml/2018/11/1/1244
> 
> Reported-by: [email-masked]
> Fixes: 1cc33161a83d ("uprobes: Support SDT markers having reference count (semaphore)")
> Signed-off-by: Ravi Bangoria <[email-masked]>

Looks good to me.

Reviewed-by: Srikar Dronamraju <[email-masked]>

> ---
>  kernel/events/uprobes.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 322e97bbb437..abbd8da9ac21 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -572,7 +572,9 @@ static void put_uprobe(struct uprobe *uprobe)
>  		 * gets called, we don't get a chance to remove uprobe from
>  		 * delayed_uprobe_list from remove_breakpoint(). Do it here.
>  		 */
> +		mutex_lock(&delayed_uprobe_lock);
>  		delayed_uprobe_remove(uprobe, NULL);
> +		mutex_unlock(&delayed_uprobe_lock);
>  		kfree(uprobe);
>  	}
>  }
> -- 
> 2.19.2
> 

-- 
Thanks and Regards
Srikar Dronamraju

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