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

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Message-ID: <CAAeHK+ydCcdtn7u=nyBDxqffk_eTKA=sOTQzTnQuNZj81HxEJQ@mail.gmail.com>
Date:   Mon, 23 Nov 2020 20:16:04 +0100
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     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>,
        Marco Elver <elver@...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 Mon, Nov 23, 2020 at 7:54 PM Andrey Konovalov <andreyknvl@...gle.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!