Re: [PATCH] Improve mutt's random data generator.

"Kevin J. McCarthy" <[email protected]> Fri, 24 Apr 2026 10:46:02 +0800

Newsgroups	gmane.mail.mutt.devel
Message-ID	<aerZahPj01Cp0LV5@qinghai>

On Thu, Apr 23, 2026 at 10:12:25PM -0400, Kurt Hackenberg wrote:
>On Fri, Apr 24, 2026 at 09:48 +0800, Kevin J. McCarthy wrote:
>
>>Ah, sorry.  Yes, the code is executed.  The whole snippet is:
>>
>> if ((res == (size_t) -1) || (res < length_requested))
>> {
>>   if (res < length_requested)
>>   {
>>     length_requested -= res;
>>     random_bytes += res;
>>   }
>>   prng_random_bytes(random_bytes, length_requested);
>> }
>
>I don't know what prng_random_bytes() is, so don't quite know the 
>intent here. But counting on (res < length_requested) when getrandom() 
>failed seems like pushing C pretty hard.

The man page says:

On success, getrandom() returns the number of bytes that were copied to 
the buffer buf.  This may be less than the number of bytes requested via 
size if either GRND_RANDOM was specified in flags and insufficient 
entropy was present in the random source or the system call was 
interrupted by a signal.

On error, -1 is returned, and errno is set to indicate the error.

So that outer "if" checks for one of two possibilities we need to 
correct for: failure (-1), or less than the number bytes requests via 
size.

The call to prng_random_bytes() was falling back on the pseudo random
generator.

However, I'm think I'll take the fallback out, and just loop the call to 
getrandom() until we fill the buffer up.  I'll send a v2 patch today or 
tomorrow.

Thanks for your feedback, Kurt and Alex!

-- 
Kevin J. McCarthy
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