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From:   Andrey Konovalov <andreyknvl@google.com>
Date:   Mon, 23 Nov 2020 20:16:04 +0100
Message-ID: <CAAeHK+ydCcdtn7u=nyBDxqffk_eTKA=sOTQzTnQuNZj81HxEJQ@mail.gmail.com>
Subject: Re: [PATCH mm v3 17/19] kasan: clean up metadata allocation and usage
To:     Dmitry Vyukov <dvyukov@google.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Alexander Potapenko <glider@google.com>,
        Marco Elver <elver@google.com>,
        Evgenii Stepanov <eugenis@google.com>,
        Branislav Rankov <Branislav.Rankov@arm.com>,
        Kevin Brodsky <kevin.brodsky@arm.com>,
        kasan-dev <kasan-dev@googlegroups.com>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Linux-MM <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Mon, Nov 23, 2020 at 7:54 PM Andrey Konovalov <andreyknvl@google.com> wrote:
>
> > > @@ -168,6 +173,9 @@ void quarantine_put(struct kmem_cache *cache, void *object)
> > >         struct qlist_head temp = QLIST_INIT;
> > >         struct kasan_free_meta *meta = kasan_get_free_meta(cache, object);
> > >
> > > +       if (!meta)
> > > +               return;
> >
> > Humm... is this possible? If yes, we would be leaking the object here...
> > Perhaps BUG_ON with a comment instead.
>
> No, this isn't possible. Will turn this into a warning and add a comment.

Actually, looking as this some more, looks like with this change this
becomes possible. I think the best approach here is to not put such
objects into quarantine, and return proper value from
____kasan_slab_free() to avoid a leak. I'll fix this in the next
version.

Thanks!