linux-kernel - Re: [RFC PATCH 20/21] crypto: deflate

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Message-ID: <CAMj1kXE4BFjracdzsM87Kq40t683RnT4VXEZjU0d0gRVwso=vA@mail.gmail.com>
Date:   Fri, 21 Jul 2023 13:17:57 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Simon Horman <simon.horman@...igine.com>
Cc:     linux-crypto@...r.kernel.org,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Eric Biggers <ebiggers@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Haren Myneni <haren@...ibm.com>,
        Nick Terrell <terrelln@...com>,
        Minchan Kim <minchan@...nel.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Jens Axboe <axboe@...nel.dk>,
        Giovanni Cabiddu <giovanni.cabiddu@...el.com>,
        Richard Weinberger <richard@....at>,
        David Ahern <dsahern@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Steffen Klassert <steffen.klassert@...unet.com>,
        linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        qat-linux@...el.com, linuxppc-dev@...ts.ozlabs.org,
        linux-mtd@...ts.infradead.org, netdev@...r.kernel.org
Subject: Re: [RFC PATCH 20/21] crypto: deflate - implement acomp API directly

On Fri, 21 Jul 2023 at 13:12, Simon Horman <simon.horman@...igine.com> wrote:
>
> On Tue, Jul 18, 2023 at 02:58:46PM +0200, Ard Biesheuvel wrote:
>
> ...
>
> > -static int deflate_comp_init(struct deflate_ctx *ctx)
> > +static int deflate_process(struct acomp_req *req, struct z_stream_s *stream,
> > +                        int (*process)(struct z_stream_s *, int))
> >  {
> > -     int ret = 0;
> > -     struct z_stream_s *stream = &ctx->comp_stream;
> > +     unsigned int slen = req->slen;
> > +     unsigned int dlen = req->dlen;
> > +     struct scatter_walk src, dst;
> > +     unsigned int scur, dcur;
> > +     int ret;
> >
> > -     stream->workspace = vzalloc(zlib_deflate_workspacesize(
> > -                             -DEFLATE_DEF_WINBITS, DEFLATE_DEF_MEMLEVEL));
> > -     if (!stream->workspace) {
> > -             ret = -ENOMEM;
> > -             goto out;
> > -     }
> > +     stream->avail_in = stream->avail_out = 0;
> > +
> > +     scatterwalk_start(&src, req->src);
> > +     scatterwalk_start(&dst, req->dst);
> > +
> > +     scur = dcur = 0;
> > +
> > +     do {
> > +             if (stream->avail_in == 0) {
> > +                     if (scur) {
> > +                             slen -= scur;
> > +
> > +                             scatterwalk_unmap(stream->next_in - scur);
> > +                             scatterwalk_advance(&src, scur);
> > +                             scatterwalk_done(&src, 0, slen);
> > +                     }
> > +
> > +                     scur = scatterwalk_clamp(&src, slen);
> > +                     if (scur) {
> > +                             stream->next_in = scatterwalk_map(&src);
> > +                             stream->avail_in = scur;
> > +                     }
> > +             }
> > +
> > +             if (stream->avail_out == 0) {
> > +                     if (dcur) {
> > +                             dlen -= dcur;
> > +
> > +                             scatterwalk_unmap(stream->next_out - dcur);
> > +                             scatterwalk_advance(&dst, dcur);
> > +                             scatterwalk_done(&dst, 1, dlen);
> > +                     }
> > +
> > +                     dcur = scatterwalk_clamp(&dst, dlen);
> > +                     if (!dcur)
> > +                             break;
>
> Hi Ard,
>
> I'm unsure if this can happen. But if this break occurs in the first
> iteration of this do loop, then ret will be used uninitialised below.
>
> Smatch noticed this.
>

Thanks.

This should not happen - it would mean req->dlen == 0, which is
rejected before this function is even called.

Whether or not it might ever happen in practice is a different matter,
of course, so I should probably initialize 'ret' to something sane.



> > +
> > +                     stream->next_out = scatterwalk_map(&dst);
> > +                     stream->avail_out = dcur;
> > +             }
> > +
> > +             ret = process(stream, (slen == scur) ? Z_FINISH : Z_SYNC_FLUSH);
> > +     } while (ret == Z_OK);
> > +
> > +     if (scur)
> > +             scatterwalk_unmap(stream->next_in - scur);
> > +     if (dcur)
> > +             scatterwalk_unmap(stream->next_out - dcur);
> > +
> > +     if (ret != Z_STREAM_END)
> > +             return -EINVAL;
> > +
> > +     req->dlen = stream->total_out;
> > +     return 0;
> > +}
>
> ...