On Mon, Aug 17, 2020 at 08:31:35PM +0200, Marco Elver wrote: > On Fri, 7 Aug 2020 at 21:06, Pekka Enberg <penberg@xxxxxxxxx> wrote: > ... > > Yeah, it reproduces with defconfig too, as long as you remember to > > pass "slub_debug=Z"... :-/ > > > > The following seems to be the culprit: > > > > commit 3202fa62fb43087387c65bfa9c100feffac74aa6 > > Author: Kees Cook <keescook@xxxxxxxxxxxx> > > Date: Wed Apr 1 21:04:27 2020 -0700 > > > > slub: relocate freelist pointer to middle of object > > > > Reverting this commit and one of it's follow up fixes from Kees from > > v5.8 makes the issue go away for me. Btw, please note that caches with > > size 24 and larger do not trigger this bug, so the issue is that with > > small enough object size, we're stomping on allocator metadata (I > > assume part of the freelist). > > Was there a patch to fix this? Checking, just in case I missed it. Hi! I've finally carved out time to look at this, and I've figured it out. My prior redzoning fix was actually wrong; I'll send a patch to fix it harder. In the meantime, I've also discovered that the redzoning code wasn't safe for sizes smaller than sizeof(void *). This oversight is, I think, what caused me to incorrectly handle the changed offset the first time. :P Anyway, patches incoming... -- Kees Cook
