linux-kernel - Re: [PATCH] fsnotify: don't put user context if it was never assigned

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Message-Id: <20140911134355.21bed9dbf5a0c7a8190c748f@linux-foundation.org>
Date:	Thu, 11 Sep 2014 13:43:55 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Sasha Levin <sasha.levin@...cle.com>
Cc:	john@...nmccutchan.com, rlove@...ve.org, eparis@...isplace.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fsnotify: don't put user context if it was never
 assigned

On Tue, 29 Jul 2014 09:25:14 -0400 Sasha Levin <sasha.levin@...cle.com> wrote:

> On some failure paths we may attempt to free user context even
> if it wasn't assigned yet. This will cause a NULL ptr deref
> and a kernel BUG.

Are you able to identify "some failure paths"?  I spent some time
grepping, but it's a pain.

Please try to include such info in changelogs because reviewers (ie,
me) might want to review those callers to decide whether the bug lies
elsewhere.

> --- a/fs/notify/inotify/inotify_fsnotify.c
> +++ b/fs/notify/inotify/inotify_fsnotify.c
> @@ -165,8 +165,10 @@ static void inotify_free_group_priv(struct fsnotify_group *group)
>  	/* ideally the idr is empty and we won't hit the BUG in the callback */
>  	idr_for_each(&group->inotify_data.idr, idr_callback, group);
>  	idr_destroy(&group->inotify_data.idr);
> -	atomic_dec(&group->inotify_data.user->inotify_devs);
> -	free_uid(group->inotify_data.user);
> +	if (group->inotify_data.user) {
> +		atomic_dec(&group->inotify_data.user->inotify_devs);
> +		free_uid(group->inotify_data.user);
> +	}
>  }
>  
>  static void inotify_free_event(struct fsnotify_event *fsn_event)

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