linux-kernel - Re: [BUGFIX PATCH] staging: ccree: save ciphertext for CTS IV

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Date:   Wed, 23 Aug 2017 09:47:07 +0200
From:   Stephan Mueller <smueller@...onox.de>
To:     Gilad Ben-Yossef <gilad@...yossef.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-crypto@...r.kernel.org,
        driverdev-devel@...uxdriverproject.org, devel@...verdev.osuosl.org,
        linux-kernel@...r.kernel.org, Ofir Drang <ofir.drang@....com>
Subject: Re: [BUGFIX PATCH] staging: ccree: save ciphertext for CTS IV

Am Mittwoch, 23. August 2017, 09:41:11 CEST schrieb Gilad Ben-Yossef:

Hi Gilad,

> 
>  	if (areq) {
> +		/*
> +		 * The crypto API expects us to set the req->info to the last
> +		 * ciphertext block. For encrypt, simply copy from the result.
> +		 * For decrypt, we must copy from a saved buffer since this
> +		 * could be an in-place decryption operation and the src is
> +		 * lost by this point.
> +		 */
> +		if (req_ctx->gen_ctx.op_type == DRV_CRYPTO_DIRECTION_DECRYPT)  {
> +			memcpy(req->info, req_ctx->backup_info, ivsize);
> +			kfree(req_ctx->backup_info);
> +		} else {
> +			scatterwalk_map_and_copy(req->info, req->dst,
> +						 (req->nbytes - ivsize),
> +						 ivsize, 0);
> +		}
> +
>  		ablkcipher_request_complete(areq, completion_error);
>  		return 0;
>  	}
> @@ -858,7 +876,6 @@ static int ssi_ablkcipher_encrypt(struct
> ablkcipher_request *req) struct blkcipher_req_ctx *req_ctx =
> ablkcipher_request_ctx(req); unsigned int ivsize =
> crypto_ablkcipher_ivsize(ablk_tfm);
> 
> -	req_ctx->backup_info = req->info;
>  	req_ctx->is_giv = false;
> 
>  	return ssi_blkcipher_process(tfm, req_ctx, req->dst, req->src,
> req->nbytes, req->info, ivsize, (void *)req, DRV_CRYPTO_DIRECTION_ENCRYPT);
> @@ -871,8 +888,18 @@ static int ssi_ablkcipher_decrypt(struct
> ablkcipher_request *req) struct blkcipher_req_ctx *req_ctx =
> ablkcipher_request_ctx(req); unsigned int ivsize =
> crypto_ablkcipher_ivsize(ablk_tfm);
> 
> -	req_ctx->backup_info = req->info;
> +	/*
> +	 * Allocate and save the last IV sized bytes of the source, which will
> +	 * be lost in case of in-place decryption and might be needed for CTS.
> +	 */
> +	req_ctx->backup_info = kmalloc(ivsize, GFP_KERNEL);
> +	if (!req_ctx->backup_info)
> +		return -ENOMEM;

Are you sure you do not add a memleak here? You seem to unconditionally 
allocate memory but conditionally free it.

Ciao
Stephan