On Sun, 9 Jul 2023, James Almer wrote:
On 7/9/2023 1:23 PM, Marton Balint wrote:
On Sun, 9 Jul 2023, Anton Khirnov wrote:
Quoting Marton Balint (2023-07-07 22:02:26)
On Fri, 7 Jul 2023, Anton Khirnov wrote:
It is a better interface for /dev/u?random on Linux, which avoids the
issues associated with opening files.
getrandom() actually have the same problem as read(). It can read less
than requested. So you should use it in a loop in that case or if it
returns EINTR.
I'm not convinced it's actually a problem.
This API is intended for small secrets like keys and such, somebody
trying to generate vast quantities of random data is likely misusing it
and could just as well use LFG or something.
Failing in that case seems like a good thing to me.
This is a very bad argument. If the API should not be used for big
secrets, then it should always fail for size > 256 or something, not
sometimes fail. And such limitation should be documented.
And its not just about big secrets. EINTR can be returned for small
secrets as well, and you should handle it.
I also question if it is a good idea to use the non blocking mode. Imagine
a situation when somebody wants to automatically start a command line
after boot which needs a key. It might fail right after boot, but will
work after a couple of minutes. IMHO it is better to block (1-2 minute
tops) than making the function sometimes work, sometimes not.
If we make the urandom/getrandom() path block and potentially take 1-2
minutes, then I'd prefer if it's last in the function, after all available
external implementations (Some of which can fail) were tried first.
It will take 1-2 minutes if it is right after boot and if the system has
no support for quickly gathering entropy via some hardware feature...
So it is not like /dev/random. It only waits until the CSPRNG of
/dev/urandom initializes. I doubt external libraries can come up something
significantly quicker, since they are also using the same system provided
randomness for initialization...
Regards,
Marton
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