Date: Fri, 23 Nov 2018 10:36:25 +0800
From: Herbert Xu <herbert@gondor.apana.org.au>
To: PanBian <bianpan2016@163.com>
Cc: "David S. Miller" <davem@davemloft.net>,
        linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] crypto: do not free algorithm before using
Message-ID: <20181123023625.oguwfmhhi2su6etr@gondor.apana.org.au>
References: <1542880816-63838-1-git-send-email-bianpan2016@163.com>
 <20181122144441.tkfmrq3lzibq2g3y@gondor.apana.org.au>
 <20181123010555.GA83154@bp>
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On Fri, Nov 23, 2018 at 09:05:55AM +0800, PanBian wrote:
>
> Thanks for your explanation! But I find that the function
> crypto_init_spawn just lets spawn->alg point to the algorithm without 
> increasing the reference count, i.e., alg->cra_refcnt. So I am confused
> about how this can protect the algorithm from being freed. Maybe I
> missed some key points. Could you please explain it in more details?

Oh you're right! This bug was introduced during the skcipher
conversion.  The spawns are not meant to carry a reference count
with them because they are not supposed to stop the underlying
algorithm from being removed.  So yes we do need to hold a reference
count on alg until the instance is registered.

Thanks,
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt