linux-kernel - Re: [PATCH 1/9] crypto: add zbufsize() interface

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Date:   Tue, 7 Aug 2018 11:10:10 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Herbert Xu <herbert@...dor.apana.org.au>
Cc:     Geliang Tang <geliangtang@...il.com>,
        Arnd Bergmann <arnd@...db.de>, Haren Myneni <haren@...ibm.com>,
        Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>,
        Zhou Wang <wangzhou1@...ilicon.com>,
        linux-crypto <linux-crypto@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/9] crypto: add zbufsize() interface

On Tue, Aug 7, 2018 at 2:45 AM, Herbert Xu <herbert@...dor.apana.org.au> wrote:
> On Thu, Aug 02, 2018 at 02:51:10PM -0700, Kees Cook wrote:
>> When pstore was refactored to use the crypto compress API in:
>>
>>   commit cb3bee0369bc ("pstore: Use crypto compress API")
>>
>> nearly all the pstore-specific compression routines were replaced with
>> the existing crypto compression API. One case remained: calculating the
>> "worst case" compression sizes ahead of time so it could have a buffer
>> preallocated for doing compression (which was called "zbufsize").
>>
>> To make pstore fully algorithm-agnostic, the compression API needs to
>> grow this functionality. This adds the interface to support querying the
>> "worst case" estimate, with a new "zbufsize" routine that each compressor
>> can implement. The per-compressor implementations come in later commits.
>>
>> Signed-off-by: Kees Cook <keescook@...omium.org>
>> ---
>>  crypto/compress.c                   |  9 +++++++++
>>  include/crypto/internal/scompress.h | 11 +++++++++++
>>  include/linux/crypto.h              | 12 ++++++++++++
>>  3 files changed, 32 insertions(+)
>>
>> diff --git a/crypto/compress.c b/crypto/compress.c
>> index f2d522924a07..29a80bb3b9d3 100644
>> --- a/crypto/compress.c
>> +++ b/crypto/compress.c
>> @@ -33,12 +33,21 @@ static int crypto_decompress(struct crypto_tfm *tfm,
>>                                                          dlen);
>>  }
>>
>> +static int crypto_zbufsize(struct crypto_tfm *tfm,
>> +                        unsigned int slen, unsigned int *dlen)
>> +{
>> +     if (!tfm->__crt_alg->cra_compress.coa_zbufsize)
>> +             return -ENOTSUPP;
>> +     return tfm->__crt_alg->cra_compress.coa_zbufsize(tfm, slen, dlen);
>> +}
>
> Please don't add new features to the old compress interface.  Any
> new improvements should be added to scomp/acomp only.  Users who
> need new features should be converted.

So, keep crypto_scomp_zbufsize() and drop crypto_comp_zbufsize() and
crypto_zbufsize()? Should I add crypto_acomp_zbufsize()?

-Kees

-- 
Kees Cook
Pixel Security