linux-kernel - Re: [PATCH resend 4.9] hw_random: Don't use a stack buffer in add_early

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Message-ID: <CALCETrVYuo1yNWyRQBRt3HwM4EJ7c5FAMZdEgnzKCHqMRCryXQ@mail.gmail.com>
Date:   Mon, 17 Oct 2016 10:30:13 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     Stephan Mueller <smueller@...onox.de>
Cc:     Andy Lutomirski <luto@...nel.org>, linux-crypto@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Matt Mackall <mpm@...enic.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Rusty Russell <rusty@...tcorp.com.au>,
        Jens Axboe <axboe@...com>, Matt Mullins <mmullins@...x.us>
Subject: Re: [PATCH resend 4.9] hw_random: Don't use a stack buffer in add_early_randomness()

On Mon, Oct 17, 2016 at 10:17 AM, Stephan Mueller <smueller@...onox.de> wrote:
> Am Montag, 17. Oktober 2016, 10:06:27 CEST schrieb Andy Lutomirski:
>
> Hi Andy,
>
>> diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
>> index 9203f2d130c0..340f96e44642 100644
>> --- a/drivers/char/hw_random/core.c
>> +++ b/drivers/char/hw_random/core.c
>> @@ -84,14 +84,14 @@ static size_t rng_buffer_size(void)
>>
>>  static void add_early_randomness(struct hwrng *rng)
>>  {
>> -     unsigned char bytes[16];
>>       int bytes_read;
>> +     size_t size = min_t(size_t, 16, rng_buffer_size());
>>
>>       mutex_lock(&reading_mutex);
>> -     bytes_read = rng_get_data(rng, bytes, sizeof(bytes), 1);
>> +     bytes_read = rng_get_data(rng, rng_buffer, size, 1);
>>       mutex_unlock(&reading_mutex);
>>       if (bytes_read > 0)
>> -             add_device_randomness(bytes, bytes_read);
>> +             add_device_randomness(rng_buffer, bytes_read);
>
> Shouldn't there be a memset(0) of the rng_buffer at this point to avoid having
> such data lingering in memory?

Sure, but shouldn't that be a separate patch covering the whole hw_crypto core?

--Andy


-- 
Andy Lutomirski
AMA Capital Management, LLC