#1012835 linux-image-5.10.0-15-amd64: entropy dropped to 256 from ~4k after 5.10.120-1 update

Package:
src:linux
Source:
linux
Submitter:
Vincas Dargis
Date:
2022-06-29 19:03:04 UTC
Severity:
normal
Tags:
#1012835#5
Date:
2022-06-15 05:05:23 UTC
From:
To:
Dear Maintainer,

I've noticed in Munin graphs that entropy dropped significantly after
reboot to 5.10.120-1. Please see images attached.

Not sure if this is actually a problem/bug, but that kind of drop "out
of nowhere" seems at least suspicious.

I see same level of entropy on multiple 5.10 machines, though on one
computers I use backported 5.16.12-1~bpo11+1 (due to issues with
i7-11700 graphics) and it's entropy looks rich:

```
$ cat /proc/sys/kernel/random/entropy_avail
3735
```

#1012835#10
Date:
2022-06-15 09:36:07 UTC
From:
To:
https://forum.openwrt.org/t/low-entropy-22-03-snapshot-change-in-kernel-entropy-pool-logic/129573

When I saw that, I check my entropy level and that was 256 too.

I *think* it's intentional; various commits in 'crypto' also in 5.10.y branch
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/log/crypto?h=linux-5.10.y

#1012835#23
Date:
2022-06-19 22:42:34 UTC
From:
To:
The most visible aspect of this, and the likely reason for several bug
reports, is that the size of the entropy pool went down from ~3000+ to 256.
This is an intentional upstream change and NOT a bug in the Debian kernel.
The 'wontfix' tag is therefor added to this bug (and therefor merged bugs).

These changes have also been backported to other LTS kernels, including
the 5.10 kernel used in Debian Bullseye.
Almost the whole upstream 5.10.119 release consist of these changes.
There have been extensive commit messages, so next to the above referenced
document, ``git log v5.10.118..v5.10.119`` should give you (more) details.