Messages in this thread | | | Date | Sun, 26 Apr 2020 08:07:27 +0800 | From | Changbin Du <> | Subject | Re: [PATCH] mm/slub: do not place freelist pointer to middle of object if redzone is on |
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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
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