crypto: qce: skcipher: Fix incorrect sg count for dma transfers

Use the sg count returned by dma_map_sg to call into
dmaengine_prep_slave_sg rather than using the original sg count. dma_map_sg
can merge consecutive sglist entries, thus making the original sg count
wrong. This is a fix for memory coruption issues observed while testing
encryption/decryption of large messages using libkcapi framework.

Patch has been tested further by running full suite of tcrypt.ko tests
including fuzz tests.
Signed-off-by: Thara Gopinath <thara.gopinath@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/crypto/qce/skcipher.c

@@ -72,7 +72,7 @@ qce_skcipher_async_req_handle(struct crypto_async_request *async_req)
 	struct scatterlist *sg;
 	bool diff_dst;
 	gfp_t gfp;
-	int ret;
+	int dst_nents, src_nents, ret;
 
 	rctx->iv = req->iv;
 	rctx->ivsize = crypto_skcipher_ivsize(skcipher);
@@ -123,21 +123,22 @@ qce_skcipher_async_req_handle(struct crypto_async_request *async_req)
 	sg_mark_end(sg);
 	rctx->dst_sg = rctx->dst_tbl.sgl;
 
-	ret = dma_map_sg(qce->dev, rctx->dst_sg, rctx->dst_nents, dir_dst);
-	if (ret < 0)
+	dst_nents = dma_map_sg(qce->dev, rctx->dst_sg, rctx->dst_nents, dir_dst);
+	if (dst_nents < 0)
 		goto error_free;
 
 	if (diff_dst) {
-		ret = dma_map_sg(qce->dev, req->src, rctx->src_nents, dir_src);
-		if (ret < 0)
+		src_nents = dma_map_sg(qce->dev, req->src, rctx->src_nents, dir_src);
+		if (src_nents < 0)
 			goto error_unmap_dst;
 		rctx->src_sg = req->src;
 	} else {
 		rctx->src_sg = rctx->dst_sg;
+		src_nents = dst_nents - 1;
 	}
 
-	ret = qce_dma_prep_sgs(&qce->dma, rctx->src_sg, rctx->src_nents,
-			       rctx->dst_sg, rctx->dst_nents,
+	ret = qce_dma_prep_sgs(&qce->dma, rctx->src_sg, src_nents,
+			       rctx->dst_sg, dst_nents,
 			       qce_skcipher_done, async_req);
 	if (ret)
 		goto error_unmap_src;