linux-kernel - Re: [PATCH v7 01/22] net/tcp: Prepare tcp_md5sig

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Message-ID: <21845b01-a915-d80a-8b87-85c6987c7691@arista.com>
Date:   Thu, 15 Jun 2023 17:44:17 +0100
From:   Dmitry Safonov <dima@...sta.com>
To:     Steen Hegelund <steen.hegelund@...rochip.com>
Cc:     David Ahern <dsahern@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        linux-kernel@...r.kernel.org,
        Andy Lutomirski <luto@...capital.net>,
        Ard Biesheuvel <ardb@...nel.org>,
        Bob Gilligan <gilligan@...sta.com>,
        Dan Carpenter <error27@...il.com>,
        David Laight <David.Laight@...lab.com>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Donald Cassidy <dcassidy@...hat.com>,
        Eric Biggers <ebiggers@...nel.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Francesco Ruggeri <fruggeri05@...il.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Ivan Delalande <colona@...sta.com>,
        Leonard Crestez <cdleonard@...il.com>,
        Salam Noureddine <noureddine@...sta.com>,
        netdev@...r.kernel.org
Subject: Re: [PATCH v7 01/22] net/tcp: Prepare tcp_md5sig_pool for TCP-AO

Hi Steen,

On 6/15/23 11:45, Steen Hegelund wrote:
> Hi Dmitry,
> 
> On Thu, 2023-06-15 at 00:09 +0100, Dmitry Safonov wrote:
[..]
>> +/**
>> + * tcp_sigpool_alloc_ahash - allocates pool for ahash requests
>> + * @alg: name of async hash algorithm
>> + * @scratch_size: reserve a tcp_sigpool::scratch buffer of this size
>> + */
>> +int tcp_sigpool_alloc_ahash(const char *alg, size_t scratch_size)
>> +{
>> +       int i, ret;
>> +
>> +       /* slow-path */
>> +       mutex_lock(&cpool_mutex);
>> +       ret = sigpool_reserve_scratch(scratch_size);
>> +       if (ret)
>> +               goto out;
>> +       for (i = 0; i < cpool_populated; i++) {
>> +               if (!cpool[i].alg)
>> +                       continue;
>> +               if (strcmp(cpool[i].alg, alg))
>> +                       continue;
>> +
>> +               if (kref_read(&cpool[i].kref) > 0)
>> +                       kref_get(&cpool[i].kref);
>> +               else
>> +                       kref_init(&cpool[i].kref);
>> +               ret = i;
>> +               goto out;
>> +       }
> 
> Here it looks to me like you will never get to this part of the code since you
> always end up going to the out label in the previous loop.

Well, not exactly: this part is looking if the crypto algorithm is
already in this pool, so that it can increment refcounter rather than
initialize a new tfm. In case strcmp(cpool[i].alg, alg) fails, this loop
will never goto out.

I.e., you issued previously setsockopt()s for TCP-MD5 and TCP-AO with
HMAC-SHA1, so in this pool there'll be two algorithms: "md5" and
"hmac(sha1)". Now if you want to use TCP-AO with "cmac(aes128)" or
"hmac(sha256)", you won't find them in the pool yet.

> 
>> +
>> +       for (i = 0; i < cpool_populated; i++) {
>> +               if (!cpool[i].alg)
>> +                       break;
>> +       }
>> +       if (i >= CPOOL_SIZE) {
>> +               ret = -ENOSPC;
>> +               goto out;
>> +       }
>> +
>> +       ret = __cpool_alloc_ahash(&cpool[i], alg);
>> +       if (!ret) {
>> +               ret = i;
>> +               if (i == cpool_populated)
>> +                       cpool_populated++;
>> +       }
>> +out:
>> +       mutex_unlock(&cpool_mutex);
>> +       return ret;
>> +}
>> +EXPORT_SYMBOL_GPL(tcp_sigpool_alloc_ahash);
>> +
> 
> ... snip ...
> 
> 
>>  clear_hash:
>> -       tcp_put_md5sig_pool();
>> -clear_hash_noput:
>> +       tcp_sigpool_end(&hp);
>> +clear_hash_nostart:
>>         memset(md5_hash, 0, 16);
>>         return 1;
>>  }
Thanks,
            Dmitry