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

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Message-ID: <54125116.9050500@oracle.com>
Date:	Thu, 11 Sep 2014 21:49:10 -0400
From:	Sasha Levin <sasha.levin@...cle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
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 09/11/2014 04:43 PM, Andrew Morton wrote:
> 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.
> 

Sorry about that.

The path I was looking at is in inotify_new_group():

        oevent = kmalloc(sizeof(struct inotify_event_info), GFP_KERNEL);
        if (unlikely(!oevent)) {
                fsnotify_destroy_group(group);
                return ERR_PTR(-ENOMEM);
        }

fsnotify_destroy_group() would get called here, but group->inotify_data.user
is only getting assigned later:

	group->inotify_data.user = get_current_user();


Thanks,
Sasha
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