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

Zero-length skcipher requests are valid no-ops, but MXS-DCP queues them.
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 <redacted>
---
 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