Re: [PATCH 12/12] config.mak.uname: add a note about CSPRNG_METHOD for Linux

> On Sun, Mar 16, 2025 at 01:41:40PM -0700, Junio C Hamano wrote:
>> "brian m. carlson" <sandals@crustytoothpaste.net> writes:
>>
>>> When arc4random was added to glibc, the Linux kernel CSPRNG maintainer
>>> argued that it was not a secure approach (I disagree), and convinced the
>>> glibc maintainers to just make it a wrapper around the Linux kernel
>>> CSPRNG, which it now is.  So there's no actual benefit to calling
>>> arc4random versus getrandom, and since it's newer and less commonly
>>> available than getrandom, as well as slightly slower (because of an
>>> extra function call), getrandom should be preferred.
>>
>> This
>>
>> https://www.phoronix.com/news/GNU-Glibc-arc4random-Functions
>>
>> was the first hit of my search in the area, but I think you are
>> referring to
>>
>> https://sourceware.org/git/?p=glibc.git;a=commitdiff;h=eaad4f9
>>
>> that happened 5 days after the thing got in and the code there tells
>> me that your summary of the situation is quite accurate.
>>
>> So I agree that dropping this patch makes sense, but do we want to
>> do a bit more to improve the situation?
>>
>> Here is an attempt to improve what we have in Makefile (and possibly
>> the Linux section in config.mak.uname, but that is improving what we
>> do not have) to tell folks that arc4random in glibc is only for
>> compatibility and they should pick getrandom() until the situation
>> changes.
>>
>> --- >8 ---
>> Subject: config/Makefile: a note on CSPRNG_METHOD choice for Linux
>>
>> arc4random() was added to glibc in July 2022, but quickly replaced
>> by a stub implementation that wraps around getrandom().  Hence there
>> is no actual benefit to calling arc4random() over getrandom() on
>> glibc based systems, at least for now.
>>
>> To avoid enticing Linux users to choose arc4random(), leave a note
>> that their arc4random() in glibc is not the same as what their
>> friends use on other platforms, and guide them to use getrandom()
>> instead in the meantime.
> 
> Makes me wonder whether we should also change the order in which Meson
> auto-detects functions. That is, do we want the following patch that
> favors getrandom over arc4random?
>