linux-kernel - Re: [PATCH] inotify: race use after free/double free in inotify inode marks

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Date:	Wed, 12 May 2010 20:16:31 -0400
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Eric Paris <eparis@...hat.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] inotify: race use after free/double free in inotify
 inode marks

On Wed, 12 May 2010 12:08:00 -0400 Eric Paris <eparis@...hat.com> wrote:

> From: root <root@...n-gt24-04.rhts.eng.bos.redhat.com>

hm.

> There is a race in the inotify add/rm watch code.  A task can find and
> remove a mark which doesn't have all of it's references.  This can
> result in a use after free/double free situation.
> 
> Task A					Task B
> ------------				-----------
> inotify_new_watch()
>  allocate a mark (refcnt == 1)
>  add it to the idr
> 					inotify_rm_watch()
> 					 inotify_remove_from_idr()
> 					  fsnotify_put_mark()
> 					      refcnt hits 0, free
>  take reference because we are on idr
>  [at this point it is a use after free]
>  [time goes on]
>  refcnt may hit 0 again, double free
> 
> The fix is to take the reference BEFORE the object can be found in the
> idr.
> 
> Signed-off-by: Eric Paris <eparis@...hat.com>

The changelog has no "Cc: <stable@...nel.org>".  I suspect it should
have that?

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