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

[Patrick Steinhardt <ps@pks.im>]

On Thu, Mar 20, 2025 at 01:28:31AM +0000, Ramsay Jones wrote:
> 
> 
> On 19/03/2025 13:30, Patrick Steinhardt wrote:
> > 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?
> > 
> 
> That was my immediate thought also. :)

Okay. Will you pick it up in v2 of this patch series?

Thanks!

Patrick