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Date:   Mon, 30 Sep 2019 15:44:05 +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: <20190930154405.00004187@huawei.com>
In-Reply-To: <20190930151702.0000131f@huawei.com>
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        <20190930151702.0000131f@huawei.com>
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On Mon, 30 Sep 2019 15:17:02 +0100
Jonathan Cameron <jonathan.cameron@huawei.com> wrote:

> 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.

Hmm. Perhaps I shouldn't review with jetlag...   That should have said
that I think the variable should be left unsigned as reality is that
it is always >= 0.

> 
> 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;  
>