[PATCH v2] crypto: mxs-dcp: handle zero-length skcipher requests

[Frank Li]

On Tue, Sep 08, 2026 at 05:44:37PM +0800, Linmao Li wrote:
> The generic ECB and CBC implementations return success for zero-length
> requests, but MXS-DCP queues them anyway. 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, matching the
> generic implementations. This avoids the invalid source access and
> leaves the IV unchanged.
>
> Fixes: fadd7a6e616b ("crypto: mxs-dcp - Fix AES issues")
> Signed-off-by: Linmao Li <lilinmao at kylinos.cn>
> ---

Reviewed-by: Frank Li <Frank.Li at nxp.com>

> v2: Clarify commit message: describe zero-length return-0 as existing
>     generic ECB/CBC behavior rather than a general API rule (Frank Li).
>  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
>