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

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  Re: [BUGFIX PATCH] staging: ccree: save ciphertext for CTS IV Stephan Mueller <smueller@chronox.de> - 2017-08-23 09:50 +0200
    Re: [BUGFIX PATCH] staging: ccree: save ciphertext for CTS IV Gilad Ben-Yossef <gilad@benyossef.com> - 2017-08-23 11:10 +0200

#1718115 — 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

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#1718176

On Wed, Aug 23, 2017 at 10:47 AM, Stephan Mueller <smueller@chronox.de> wrote:
> 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.

You are right. I've missed freeing the memory on error code paths.
Thank you for catching that.
The code involved is badly need of a re-write but I wanted to get the
obvious bug fixed first.
I will send a revised patch

Thanks,
Gilad




-- 
Gilad Ben-Yossef
Chief Coffee Drinker

"If you take a class in large-scale robotics, can you end up in a
situation where the homework eats your dog?"
 -- Jean-Baptiste Queru

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