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

[Linmao Li]

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@xxxxxxxxxx. 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,
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@xxxxxxxxxx>
> > ---
> >   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