netdev - Re: [PATCH 2/2] crypto: Remove unnecessary memzero

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Message-ID: <7e13a94b-2e92-850f-33f7-0f42cfcd9009@redhat.com>
Date:   Mon, 13 Apr 2020 17:52:24 -0400
From:   Waiman Long <longman@...hat.com>
To:     Joe Perches <joe@...ches.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Howells <dhowells@...hat.com>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        David Rientjes <rientjes@...gle.com>
Cc:     linux-mm@...ck.org, keyrings@...r.kernel.org,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-crypto@...r.kernel.org, linux-s390@...r.kernel.org,
        linux-pm@...r.kernel.org, linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org,
        linux-amlogic@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linuxppc-dev@...ts.ozlabs.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
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        linux-fscrypt@...r.kernel.org, ecryptfs@...r.kernel.org,
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        linux-integrity@...r.kernel.org
Subject: Re: [PATCH 2/2] crypto: Remove unnecessary memzero_explicit()

On 4/13/20 5:31 PM, Joe Perches wrote:
> On Mon, 2020-04-13 at 17:15 -0400, Waiman Long wrote:
>> Since kfree_sensitive() will do an implicit memzero_explicit(), there
>> is no need to call memzero_explicit() before it. Eliminate those
>> memzero_explicit() and simplify the call sites.
> 2 bits of trivia:
>
>> diff --git a/drivers/crypto/allwinner/sun8i-ce/sun8i-ce-cipher.c b/drivers/crypto/allwinner/sun8i-ce/sun8i-ce-cipher.c
> []
>> @@ -391,10 +388,7 @@ int sun8i_ce_aes_setkey(struct crypto_skcipher *tfm, const u8 *key,
>>  		dev_dbg(ce->dev, "ERROR: Invalid keylen %u\n", keylen);
>>  		return -EINVAL;
>>  	}
>> -	if (op->key) {
>> -		memzero_explicit(op->key, op->keylen);
>> -		kfree(op->key);
>> -	}
>> +	kfree_sensitive(op->key);
>>  	op->keylen = keylen;
>>  	op->key = kmemdup(key, keylen, GFP_KERNEL | GFP_DMA);
>>  	if (!op->key)
> It might be a defect to set op->keylen before the kmemdup succeeds.
It could be. I can move it down after the op->key check.
>> @@ -416,10 +410,7 @@ int sun8i_ce_des3_setkey(struct crypto_skcipher *tfm, const u8 *key,
>>  	if (err)
>>  		return err;
>>  
>> -	if (op->key) {
>> -		memzero_explicit(op->key, op->keylen);
>> -		kfree(op->key);
>> -	}
>> +	free_sensitive(op->key, op->keylen);
> Why not kfree_sensitive(op->key) ?

Oh, it is a bug. I will send out v2 to fix that.

Thanks for spotting it.

Cheers,
Longman


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