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Re: [PATCH 1/1] mm/slub.c: add a naive detection of double free or corruption

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On Mon, 17 Jul 2017, Matthew Wilcox wrote:

> On Mon, Jul 17, 2017 at 07:45:07PM +0300, Alexander Popov wrote:
> > Add an assertion similar to "fasttop" check in GNU C Library allocator:
> > an object added to a singly linked freelist should not point to itself.
> > That helps to detect some double free errors (e.g. CVE-2017-2636) without
> > slub_debug and KASAN. Testing with hackbench doesn't show any noticeable
> > performance penalty.
>
> >  {
> > +	BUG_ON(object == fp); /* naive detection of double free or corruption */
> >  	*(void **)(object + s->offset) = fp;
> >  }
>
> Is BUG() the best response to this situation?  If it's a corruption, then
> yes, but if we spot a double-free, then surely we should WARN() and return
> without doing anything?

The double free debug checking already does the same thing in a more
thourough way (this one only checks if the last free was the same
address). So its duplicating a check that already exists. However, this
one is always on.

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[PATCH 1/1] mm/slub.c: add a naive detection of double free or corruption Alexander Popov <alex.popov@linux.com> - 2017-07-17 18:50 +0200
  Re: [PATCH 1/1] mm/slub.c: add a naive detection of double free or  corruption Christopher Lameter <cl@linux.com> - 2017-07-17 19:00 +0200
  Re: [PATCH 1/1] mm/slub.c: add a naive detection of double free or  corruption Matthew Wilcox <willy@infradead.org> - 2017-07-17 20:00 +0200
    Re: [PATCH 1/1] mm/slub.c: add a naive detection of double free or  corruption Christopher Lameter <cl@linux.com> - 2017-07-17 20:20 +0200
      Re: [PATCH 1/1] mm/slub.c: add a naive detection of double free or  corruption Alexander Popov <alex.popov@linux.com> - 2017-07-17 21:10 +0200
        Re: [PATCH 1/1] mm/slub.c: add a naive detection of double free or corruption Kees Cook <keescook@chromium.org> - 2017-07-17 21:20 +0200
    Re: [PATCH 1/1] mm/slub.c: add a naive detection of double free or  corruption Alexander Popov <alex.popov@linux.com> - 2017-07-17 20:30 +0200

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