crypto: atmel-aes - Fix IV handling when req->nbytes < ivsize

commit 394a9e04 ("crypto: cfb - add missing 'chunksize' property")
adds a test vector where the input length is smaller than the IV length
(the second test vector). This revealed a NULL pointer dereference in
the atmel-aes driver, that is caused by passing an incorrect offset in
scatterwalk_map_and_copy() when atmel_aes_complete() is called.

Do not save the IV in req->info of ablkcipher_request (or equivalently
req->iv of skcipher_request) when req->nbytes < ivsize, because the IV
will not be further used.

While touching the code, modify the type of ivsize from int to
unsigned int, to comply with the return type of
crypto_ablkcipher_ivsize().

Fixes: 91308019 ("crypto: atmel-aes - properly set IV after {en,de}crypt")
Cc: <stable@vger.kernel.org>
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/crypto/atmel-aes.c

@@ -490,6 +490,29 @@ static inline bool atmel_aes_is_encrypt(const struct atmel_aes_dev *dd)
 static void atmel_aes_authenc_complete(struct atmel_aes_dev *dd, int err);
 #endif
 
+static void atmel_aes_set_iv_as_last_ciphertext_block(struct atmel_aes_dev *dd)
+{
+	struct ablkcipher_request *req = ablkcipher_request_cast(dd->areq);
+	struct atmel_aes_reqctx *rctx = ablkcipher_request_ctx(req);
+	struct crypto_ablkcipher *ablkcipher = crypto_ablkcipher_reqtfm(req);
+	unsigned int ivsize = crypto_ablkcipher_ivsize(ablkcipher);
+
+	if (req->nbytes < ivsize)
+		return;
+
+	if (rctx->mode & AES_FLAGS_ENCRYPT) {
+		scatterwalk_map_and_copy(req->info, req->dst,
+					 req->nbytes - ivsize, ivsize, 0);
+	} else {
+		if (req->src == req->dst)
+			memcpy(req->info, rctx->lastc, ivsize);
+		else
+			scatterwalk_map_and_copy(req->info, req->src,
+						 req->nbytes - ivsize,
+						 ivsize, 0);
+	}
+}
+
 static inline int atmel_aes_complete(struct atmel_aes_dev *dd, int err)
 {
 #ifdef CONFIG_CRYPTO_DEV_ATMEL_AUTHENC
@@ -500,26 +523,8 @@ static inline int atmel_aes_complete(struct atmel_aes_dev *dd, int err)
 	clk_disable(dd->iclk);
 	dd->flags &= ~AES_FLAGS_BUSY;
 
-	if (!dd->ctx->is_aead) {
-		struct ablkcipher_request *req =
-			ablkcipher_request_cast(dd->areq);
-		struct atmel_aes_reqctx *rctx = ablkcipher_request_ctx(req);
-		struct crypto_ablkcipher *ablkcipher =
-			crypto_ablkcipher_reqtfm(req);
-		int ivsize = crypto_ablkcipher_ivsize(ablkcipher);
-
-		if (rctx->mode & AES_FLAGS_ENCRYPT) {
-			scatterwalk_map_and_copy(req->info, req->dst,
-				req->nbytes - ivsize, ivsize, 0);
-		} else {
-			if (req->src == req->dst) {
-				memcpy(req->info, rctx->lastc, ivsize);
-			} else {
-				scatterwalk_map_and_copy(req->info, req->src,
-					req->nbytes - ivsize, ivsize, 0);
-			}
-		}
-	}
+	if (!dd->ctx->is_aead)
+		atmel_aes_set_iv_as_last_ciphertext_block(dd);
 
 	if (dd->is_async)
 		dd->areq->complete(dd->areq, err);
@@ -1125,10 +1130,12 @@ static int atmel_aes_crypt(struct ablkcipher_request *req, unsigned long mode)
 	rctx->mode = mode;
 
 	if (!(mode & AES_FLAGS_ENCRYPT) && (req->src == req->dst)) {
-		int ivsize = crypto_ablkcipher_ivsize(ablkcipher);
+		unsigned int ivsize = crypto_ablkcipher_ivsize(ablkcipher);
 
-		scatterwalk_map_and_copy(rctx->lastc, req->src,
-			(req->nbytes - ivsize), ivsize, 0);
+		if (req->nbytes >= ivsize)
+			scatterwalk_map_and_copy(rctx->lastc, req->src,
+						 req->nbytes - ivsize,
+						 ivsize, 0);
 	}
 
 	return atmel_aes_handle_queue(dd, &req->base);