Re: [bug, netconsole, SLUB] BUG skbuff_head_cache: Poisonoverwritten

From: Ingo Molnar
Date: Fri Jul 18 2008 - 05:10:42 EST

* Pekka Enberg <penberg@xxxxxxxxxxxxxx> wrote:

> On Fri, Jul 18, 2008 at 8:46 AM, Evgeniy Polyakov <johnpol@xxxxxxxxxxx> wrote:
> > Does SLUB have a debug check at freeing time? If so, how does it work
> > and why didn't it caught use after free there?
> You can't detect use after free before the object is actually free'd
> ;-)

yeah, we want to check use-after free at the next allocation point -
i.e. as late as possible to gather all corruptions that happened

We could in theory have a SLUB debug mode where a SCHED_IDLE kernel
thread would periodically check all free objects (of that CPU) in the
background to ensure their integrity. That would catch corruptions
sooner, with a possibly still meaningful context to print out. [right
after the IRQ or process that corrupts them finishes running]

It could also be hooked into ftrace to print out the last few hundred
kernel function calls executed prior any corruption. ftrace/slub-debug
plugin perhaps?

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