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

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 <redacted>
---
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