linux-kernel - Re: [syzbot] [crypto?] general protection fault in scatterwalk

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Message-ID: <CAGsJ_4zwd71VmDsErFG-2=V8aqP9dc2qO_hRNcHPj51=CfTJww@mail.gmail.com>
Date: Thu, 28 Dec 2023 09:43:19 +0800
From: Barry Song <21cnbao@...il.com>
To: Nhat Pham <nphamcs@...il.com>
Cc: Chengming Zhou <zhouchengming@...edance.com>, Chris Li <chrisl@...nel.org>, 
	syzbot <syzbot+3eff5e51bf1db122a16e@...kaller.appspotmail.com>, 
	akpm@...ux-foundation.org, davem@...emloft.net, herbert@...dor.apana.org.au, 
	linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org, 
	syzkaller-bugs@...glegroups.com, yosryahmed@...gle.com
Subject: Re: [syzbot] [crypto?] general protection fault in
 scatterwalk_copychunks (5)

On Thu, Dec 28, 2023 at 7:26 AM Nhat Pham <nphamcs@...il.com> wrote:
>
> On Wed, Dec 27, 2023 at 3:10 AM Barry Song <21cnbao@...il.com> wrote:
> >
> > On Wed, Dec 27, 2023 at 5:16 PM Chengming Zhou
> > <zhouchengming@...edance.com> wrote:
> > >
> > > Thanks for your explanation! Maybe it's best for us to return to 2 pages
> > > if no other people's comments. And this really need more documentation :-)
>
> 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 = 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 = size_to_chunks(size);
        struct z3fold_header *zhdr = NULL;
        struct page *page = NULL;
        enum buddy bud;
        bool can_sleep = 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