Messages in this thread | | | Subject | Re: [origin tree SLAB corruption] BUG kmalloc-64: Poison overwritten, INFO: Allocated in bdi_alloc_work+0x2b/0x100 age=175 cpu=1 pid=3514 | From | Pekka Enberg <> | Date | Mon, 14 Sep 2009 12:23:16 +0300 |
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On Mon, 2009-09-14 at 11:20 +0200, Jens Axboe wrote: > On Mon, Sep 14 2009, Pekka Enberg wrote: > > * Eric Paris <eparis@redhat.com> wrote: > > >> On Sat, 2009-09-12 at 09:24 +0200, Ingo Molnar wrote: > > >> > James - i did not see a security pull request email from you in my > > >> > lkml folder so i created this new thread. -tip testing found the > > >> > easy crash below. It reverts cleanly so i went that easy route. > > >> > > > >> > At a really quick 10-seconds glance the crash happens because we > > >> > destroy the slab cache twice, if the sysctl is toggled twice? > > >> > > >> Something a lot worse than SELinux here. I added this exact code and > > >> got this warning. Something is wrong in the world of > > >> kmem_cache_destroy..... > > > > Btw, the kmem_cache_destroy() bug Eric found is not in Linu's tree yet. > > > > On Mon, Sep 14, 2009 at 10:16 AM, Ingo Molnar <mingo@elte.hu> wrote: > > > -tip testing just triggered another type of SLAB problem (this time > > > not apparently related to the security subsystem): > > > > > > BUG kmalloc-64: Poison overwritten > > > ----------------------------------------------------------------------------- > > > > > > INFO: 0xf498f6a0-0xf498f6a7. First byte 0x90 instead of 0x6b > > > INFO: Allocated in bdi_alloc_work+0x2b/0x100 age=175 cpu=1 pid=3514 > > > INFO: Freed in bdi_work_free+0x45/0x60 age=9 cpu=1 pid=3509 > > > INFO: Slab 0xc3257d84 objects=36 used=11 fp=0xf498f690 flags=0x400000c3 > > > INFO: Object 0xf498f690 @offset=1680 fp=0xf498fe00 > > > > > > Bytes b4 0xf498f680: ab 0d 00 00 9c 27 ff ff 5a 5a 5a 5a 5a 5a 5a 5a «....'ÿÿZZZZZZZZ > > > Object 0xf498f690: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk > > > Object 0xf498f6a0: 90 f3 98 f4 60 3c 11 c1 6b 6b 6b 6b 6b 6b 6b 6b .ó.ô`<.Ákkkkkkkk > > > > This would be use-after-free in kmalloc-64 cache. Given the trace and > > the fact that bdi_work_alloc() got introduce recently, it seems more > > likely that fs/fs-writeback.c is to blame here. Jens, does the warning > > ring a bell to you? > > No bells, the code seems right to me. I'll prod at it a bit more. I > haven't seen anything like this during testing.
OK, it's possible that someone else is holding on to the kmalloc-64 memory block too but that won't show up in the traces.
Pekka
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