linux-kernel - Re: [PATCH] crypto: do not free algorithm before using

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Message-ID: <20181123023625.oguwfmhhi2su6etr@gondor.apana.org.au>
Date:   Fri, 23 Nov 2018 10:36:25 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     PanBian <bianpan2016@....com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] crypto: do not free algorithm before using

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@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt