bug#31268: 'guix system vm-image' hangs

[ludo@gnu.org (Ludovic Courtès)]

Hi!

Clément Lassieur <clement@lassieur.org> skribis:

> Mark H Weaver <mhw@netris.org> writes:

[...]

>> I suggest doing a git bisect on the 4.16.y branch of the linux-stable
>> git repository, between the 4.16.3 and 4.16.4 tags.
>
> I did it, here is the result:

Impressive, thanks a lot!  Did you have a script to do that or
something?

> cd8d7a5778a4abf76ee8fe8f1bfcf78976029f8d is the first bad commit
> commit cd8d7a5778a4abf76ee8fe8f1bfcf78976029f8d
> Author: Theodore Ts'o <tytso@mit.edu>
> Date:   Wed Apr 11 13:27:52 2018 -0400
>
>     random: fix crng_ready() test
>     
>     commit 43838a23a05fbd13e47d750d3dfd77001536dd33 upstream.
>     
>     The crng_init variable has three states:
>     
>     0: The CRNG is not initialized at all
>     1: The CRNG has a small amount of entropy, hopefully good enough for
>        early-boot, non-cryptographical use cases
>     2: The CRNG is fully initialized and we are sure it is safe for
>        cryptographic use cases.
>     
>     The crng_ready() function should only return true once we are in the
>     last state.  This addresses CVE-2018-1108.

What happens I think is that libparted/fs/r/fat/fat.c:fat_create calls
‘generate_random_uint32’, which in turn indirectly calls
‘get_random_bytes’ from libuuid (package ‘e2fsprogs’).  And I suppose
that’s where it blocks, even though it’s supposed to be using
/dev/urandom, which is not supposed to block.

To be continued…

Ludo’.