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From: Barry Song <21cnbao@gmail.com>
Date: Thu, 28 Dec 2023 09:43:19 +0800
Message-ID: <CAGsJ_4zwd71VmDsErFG-2=V8aqP9dc2qO_hRNcHPj51=CfTJww@mail.gmail.com>
Subject: Re: [syzbot] [crypto?] general protection fault in
 scatterwalk_copychunks (5)
To: Nhat Pham <nphamcs@gmail.com>
Cc: Chengming Zhou <zhouchengming@bytedance.com>, Chris Li <chrisl@kernel.org>, 
	syzbot <syzbot+3eff5e51bf1db122a16e@syzkaller.appspotmail.com>, 
	akpm@linux-foundation.org, davem@davemloft.net, herbert@gondor.apana.org.au, 
	linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org, 
	syzkaller-bugs@googlegroups.com, yosryahmed@google.com
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On Thu, Dec 28, 2023 at 7:26=E2=80=AFAM Nhat Pham <nphamcs@gmail.com> wrote=
:
>
> On Wed, Dec 27, 2023 at 3:10=E2=80=AFAM Barry Song <21cnbao@gmail.com> wr=
ote:
> >
> > On Wed, Dec 27, 2023 at 5:16=E2=80=AFPM Chengming Zhou
> > <zhouchengming@bytedance.com> wrote:
> > >
> > > Thanks for your explanation! Maybe it's best for us to return to 2 pa=
ges
> > > if no other people's comments. And this really need more documentatio=
n :-)
>
> Fine by me. Hmm we're basically wasting one extra page per CPU (since
> these buffers are per-CPU), correct? That's not ideal, but not *too*
> bad for now I suppose...
>
> >
> > I agree. we need some doc.
> >
> > besides, i actually think we can skip zswap frontend if
> > over-compression is really
> > happening.
>
> IIUC, zsmalloc already checked that - and most people are (or should
> be) using zsmalloc for zswap anyway. I wouldn't be opposed to adding
> an added layer of protection on the zswap side, but not super high
> priority I'd say.

Thanks for this info. I guess you mean the below ?
unsigned long zs_malloc(struct zs_pool *pool, size_t size, gfp_t gfp)
{
        ...

        if (unlikely(!size || size > ZS_MAX_ALLOC_SIZE))
                return (unsigned long)ERR_PTR(-EINVAL);

}

i find zbud also has similar code:
static int zbud_alloc(struct zbud_pool *pool, size_t size, gfp_t gfp,
                        unsigned long *handle)
{
        int chunks, i, freechunks;
        struct zbud_header *zhdr =3D NULL;
        enum buddy bud;
        struct page *page;

        if (!size || (gfp & __GFP_HIGHMEM))
                return -EINVAL;
        if (size > PAGE_SIZE - ZHDR_SIZE_ALIGNED - CHUNK_SIZE)
                return -ENOSPC;

and z3fold,

static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp,
                        unsigned long *handle)
{
        int chunks =3D size_to_chunks(size);
        struct z3fold_header *zhdr =3D NULL;
        struct page *page =3D NULL;
        enum buddy bud;
        bool can_sleep =3D gfpflags_allow_blocking(gfp);

        if (!size || (gfp & __GFP_HIGHMEM))
                return -EINVAL;

        if (size > PAGE_SIZE)
                return -ENOSPC;


Thus, I agree that another layer to check size in zswap isn't necessary now=
.


Thanks
Barry