[PATCH] crypto: mxs-dcp: handle zero-length skcipher requests

[Frank Li]

On Mon, Aug 31, 2026 at 08:42:20PM +0800, Linmao Li wrote:
> [You don't often get email from lilinmao at kylinos.cn. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]
>
> 在 2026/8/29 3:25, Frank Li 写道:
> > On Fri, Aug 28, 2026 at 05:32:09PM +0800, Linmao Li wrote:
> > > [You don't often get email from lilinmao at kylinos.cn. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]
> > >
> > > Zero-length skcipher requests are valid no-ops, but MXS-DCP queues them.
> > Any document show it? if return 0 when cryptelen, it is async, no
> > call crypto_request_complete.
>   Yes. CRYPTO_ALG_ASYNC means that the implementation may complete a
>   request asynchronously, not that every request must do so.
>
>   A return value of 0 indicates synchronous completion.  Only
>   -EINPROGRESS and -EBUSY cause crypto_wait_req() to wait for the
>   completion callback.  The existing fallback path relies on the same
>   semantics.
>
>   There is also a direct precedent in commit 8a4e047c6cc0
>   ("crypto: marvell/cesa - Handle zero-length skcipher requests").
>   Marvell CESA registers asynchronous skcipher algorithms but handles a
>   zero-length request with:
>
>           if (!req->cryptlen)
>                   return 0;

Thanks, but still not answer my question,

Any document show "Zero-length skcipher requests are valid no-ops", why
not API direct return 0, instead of pass to every driver to check it.

I suppose it should be checked before call driver's callback.

Frank

>
>
> Thanks,
> Linmao
>
> >
> > Frank
> >
> > > When such a request reaches the worker, last_out_len remains zero. The
> > > CBC completion path then subtracts AES_BLOCK_SIZE from this unsigned
> > > value when updating the IV, causing the offset to underflow. On
> > > decryption, the resulting source address precedes aes_in_buf.
> > >
> > > Return success before enqueueing zero-length requests. This avoids the
> > > invalid source access and leaves the IV unchanged for a no-op.
> > >
> > > Fixes: fadd7a6e616b ("crypto: mxs-dcp - Fix AES issues")
> > > Signed-off-by: Linmao Li <lilinmao at kylinos.cn>
> > > ---
> > >   drivers/crypto/mxs-dcp.c | 3 +++
> > >   1 file changed, 3 insertions(+)
> > >
> > > diff --git a/drivers/crypto/mxs-dcp.c b/drivers/crypto/mxs-dcp.c
> > > index 133ebc998236..60794b4d49fa 100644
> > > --- a/drivers/crypto/mxs-dcp.c
> > > +++ b/drivers/crypto/mxs-dcp.c
> > > @@ -473,6 +473,9 @@ static int mxs_dcp_aes_enqueue(struct skcipher_request *req, int enc, int ecb)
> > >          struct dcp_aes_req_ctx *rctx = skcipher_request_ctx(req);
> > >          int ret;
> > >
> > > +       if (!req->cryptlen)
> > > +               return 0;
> > > +
> > >          if (unlikely(actx->key_len != AES_KEYSIZE_128 && !actx->key_referenced))
> > >                  return mxs_dcp_block_fallback(req, enc);
> > >
> > >
> > > base-commit: 8d3ae59288f1e7d58d76558a6ee96d533bc5019f
> > > --
> > > 2.25.1
> > >
> > >