crypto: xts - Handle EBUSY correctly

As it is xts only handles the special return value of EINPROGRESS,
which means that in all other cases it will free data related to the
request.

However, as the caller of xts may specify MAY_BACKLOG, we also need
to expect EBUSY and treat it in the same way.  Otherwise backlogged
requests will trigger a use-after-free.

Fixes: 8083b1bf ("crypto: xts - add support for ciphertext stealing")
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/xts.c

@@ -203,12 +203,12 @@ static void xts_encrypt_done(struct crypto_async_request *areq, int err)
 	if (!err) {
 		struct xts_request_ctx *rctx = skcipher_request_ctx(req);
 
-		rctx->subreq.base.flags &= ~CRYPTO_TFM_REQ_MAY_SLEEP;
+		rctx->subreq.base.flags &= CRYPTO_TFM_REQ_MAY_BACKLOG;
 		err = xts_xor_tweak_post(req, true);
 
 		if (!err && unlikely(req->cryptlen % XTS_BLOCK_SIZE)) {
 			err = xts_cts_final(req, crypto_skcipher_encrypt);
-			if (err == -EINPROGRESS)
+			if (err == -EINPROGRESS || err == -EBUSY)
 				return;
 		}
 	}
@@ -223,12 +223,12 @@ static void xts_decrypt_done(struct crypto_async_request *areq, int err)
 	if (!err) {
 		struct xts_request_ctx *rctx = skcipher_request_ctx(req);
 
-		rctx->subreq.base.flags &= ~CRYPTO_TFM_REQ_MAY_SLEEP;
+		rctx->subreq.base.flags &= CRYPTO_TFM_REQ_MAY_BACKLOG;
 		err = xts_xor_tweak_post(req, false);
 
 		if (!err && unlikely(req->cryptlen % XTS_BLOCK_SIZE)) {
 			err = xts_cts_final(req, crypto_skcipher_decrypt);
-			if (err == -EINPROGRESS)
+			if (err == -EINPROGRESS || err == -EBUSY)
 				return;
 		}
 	}