crypto: qce - save a sg table slot for result buf

When ctr-aes-qce is used for gcm-mode, an extra sg entry for the
authentication tag is present, causing trouble when the qce driver
prepares the dst-results sg table for dma.

It computes the number of entries needed with sg_nents_for_len, leaving
out the tag entry.  Then it creates a sg table with that number plus
one, used to store a result buffer.

When copying the sg table, there's no limit to the number of entries
copied, so the extra slot is filled with the authentication tag sg.
When the driver tries to add the result sg, the list is full, and it
returns EINVAL.

By limiting the number of sg entries copied to the dest table, the slot
for the result buffer is guaranteed to be unused.

Signed-off-by: Eneas U de Queiroz <cotequeiroz@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/crypto/qce/dma.c

@@ -47,7 +47,8 @@ void qce_dma_release(struct qce_dma_data *dma)
 }
 
 struct scatterlist *
-qce_sgtable_add(struct sg_table *sgt, struct scatterlist *new_sgl)
+qce_sgtable_add(struct sg_table *sgt, struct scatterlist *new_sgl,
+		int max_ents)
 {
 	struct scatterlist *sg = sgt->sgl, *sg_last = NULL;
 
@@ -60,12 +61,13 @@ qce_sgtable_add(struct sg_table *sgt, struct scatterlist *new_sgl)
 	if (!sg)
 		return ERR_PTR(-EINVAL);
 
-	while (new_sgl && sg) {
+	while (new_sgl && sg && max_ents) {
 		sg_set_page(sg, sg_page(new_sgl), new_sgl->length,
 			    new_sgl->offset);
 		sg_last = sg;
 		sg = sg_next(sg);
 		new_sgl = sg_next(new_sgl);
+		max_ents--;
 	}
 
 	return sg_last;

drivers/crypto/qce/dma.h

@@ -42,6 +42,7 @@ int qce_dma_prep_sgs(struct qce_dma_data *dma, struct scatterlist *sg_in,
 void qce_dma_issue_pending(struct qce_dma_data *dma);
 int qce_dma_terminate_all(struct qce_dma_data *dma);
 struct scatterlist *
-qce_sgtable_add(struct sg_table *sgt, struct scatterlist *sg_add);
+qce_sgtable_add(struct sg_table *sgt, struct scatterlist *sg_add,
+		int max_ents);
 
 #endif /* _DMA_H_ */

drivers/crypto/qce/skcipher.c

@@ -95,13 +95,13 @@ qce_skcipher_async_req_handle(struct crypto_async_request *async_req)
 
 	sg_init_one(&rctx->result_sg, qce->dma.result_buf, QCE_RESULT_BUF_SZ);
 
-	sg = qce_sgtable_add(&rctx->dst_tbl, req->dst);
+	sg = qce_sgtable_add(&rctx->dst_tbl, req->dst, rctx->dst_nents - 1);
 	if (IS_ERR(sg)) {
 		ret = PTR_ERR(sg);
 		goto error_free;
 	}
 
-	sg = qce_sgtable_add(&rctx->dst_tbl, &rctx->result_sg);
+	sg = qce_sgtable_add(&rctx->dst_tbl, &rctx->result_sg, 1);
 	if (IS_ERR(sg)) {
 		ret = PTR_ERR(sg);
 		goto error_free;