Received-SPF: pass (google.com: best guess record for domain of linux-crypto-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Mon, 30 Sep 2019 15:17:02 +0100
From:   Jonathan Cameron <jonathan.cameron@huawei.com>
To:     Tian Tao <tiantao6@huawei.com>
CC:     <gilad@benyossef.com>, <herbert@gondor.apana.org.au>,
        <davem@davemloft.net>, <linux-crypto@vger.kernel.org>,
        <linuxarm@huawei.com>
Subject: Re: [PATCH] crypto: fix comparison of unsigned expression warnings
Message-ID: <20190930151702.0000131f@huawei.com>
In-Reply-To: <1569833361-47224-1-git-send-email-tiantao6@huawei.com>
References: <1569833361-47224-1-git-send-email-tiantao6@huawei.com>
Organization: Huawei
MIME-Version: 1.0
Content-Type: text/plain; charset="US-ASCII"
Content-Transfer-Encoding: 7bit
Sender: linux-crypto-owner@vger.kernel.org
Precedence: bulk

On Mon, 30 Sep 2019 16:49:21 +0800
Tian Tao <tiantao6@huawei.com> wrote:

> This patch fixes the following warnings:
> drivers/crypto/ccree/cc_aead.c:630:5-12: WARNING: Unsigned expression
> compared with zero: seq_len > 0
> 
> Signed-off-by: Tian Tao <tiantao6@huawei.com>

Apologies, I should have looked into this in more depth when you asked
me about it earlier rather than assuming it was 'obviously' the right
fix.

It's more complex than I expected given the warning, which I note
is > 0 so it's not always true.  I'm curious, which compiler generates
that warning?

So there are two ways seq_len can be set to non 0, hmac_setkey which returns a
signed int, but one that is reality is >= 0. The other is xcbc_setkey
which returns an unsigned int.

So I would suggest that in addition to what you have here, a change
to the return type of hmac_setkey in order to make it clear that
never returns a negative anyway.

Can also use if (seq_len)
rather than if (seq_len > 0)

Thanks,

Jonathan


> ---
>  drivers/crypto/ccree/cc_aead.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/crypto/ccree/cc_aead.c b/drivers/crypto/ccree/cc_aead.c
> index d3e8faa..b19291d 100644
> --- a/drivers/crypto/ccree/cc_aead.c
> +++ b/drivers/crypto/ccree/cc_aead.c
> @@ -546,7 +546,7 @@ static int cc_aead_setkey(struct crypto_aead *tfm, const u8 *key,
>  	struct cc_aead_ctx *ctx = crypto_aead_ctx(tfm);
>  	struct cc_crypto_req cc_req = {};
>  	struct cc_hw_desc desc[MAX_AEAD_SETKEY_SEQ];
> -	unsigned int seq_len = 0;
> +	int seq_len = 0;
>  	struct device *dev = drvdata_to_dev(ctx->drvdata);
>  	const u8 *enckey, *authkey;
>  	int rc;