lkml.org 
[lkml]   [2020]   [Apr]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] mm/slub: do not place freelist pointer to middle of object if redzone is on
Hi Kees,
On Sat, Apr 25, 2020 at 03:48:31PM -0700, Kees Cook wrote:
> On Sat, Apr 25, 2020 at 05:13:38PM +0800, Changbin Du wrote:
> > The recent kernel fails to boot when slub redzone is turned on. This is
> > caused by commit 3202fa62fb ("slub: relocate freelist pointer to middle of
> > object") which relocates freelist pointer to middle of object. In this
> > case, get_track() gets a wrong address and then the redzone is overwritten.
>
> Hi! A fix for this is already in -next:
>
> https://www.ozlabs.org/~akpm/mmotm/broken-out/slub-avoid-redzone-when-choosing-freepointer-location.patch
>
> the above doesn't disable the mitigation when using redzones, so I
> prefer that to this suggested solution.
>
Glade to see it's been reported. But I am sorry that your patch cannot fix it.

With your fix, I suppose the layout of slub is:
|obj-fp-obj|redzone|track|...

While get_track():
p = object + s->offset + sizeof(void *);

Then we still get a wrong location. I just tested linux-next and the problem is
still there.

Is the right and left redzone good enough to protect the freepointer? If not,
I will send a patch to fix get_track() along with your patch.

> --
> Kees Cook

--
Cheers,
Changbin Du

\
 
 \ /
  Last update: 2020-04-26 02:08    [W:0.805 / U:0.516 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site