linux-kernel - Re: [PATCH mm v3 17/19] kasan: clean up metadata allocation and usage

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Date:   Tue, 17 Nov 2020 14:18:32 +0100
From:   Marco Elver <elver@...gle.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Andrey Konovalov <andreyknvl@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Evgenii Stepanov <eugenis@...gle.com>,
        Branislav Rankov <Branislav.Rankov@....com>,
        Kevin Brodsky <kevin.brodsky@....com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH mm v3 17/19] kasan: clean up metadata allocation and usage

On Tue, 17 Nov 2020 at 14:12, Dmitry Vyukov <dvyukov@...gle.com> wrote:

> > +        */
> >         *(u8 *)kasan_mem_to_shadow(object) = KASAN_KMALLOC_FREE;
> > +
> >         ___cache_free(cache, object, _THIS_IP_);
> >
> >         if (IS_ENABLED(CONFIG_SLAB))
> > @@ -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.

If this is possible in prod-mode KASAN, a WARN_ON() that returns would be safer.