Bug#1037138: linux-image-6.0.0-4-amd64: Linux kernel appears to not be respecting sysctl config value "net.ipv6.conf.all.disable_ipv6=1"

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From	Salvatore Bonaccorso <carnil@debian.org>
Newsgroups	linux.debian.bugs.dist, linux.debian.kernel
Subject	Bug#1037138: linux-image-6.0.0-4-amd64: Linux kernel appears to not be respecting sysctl config value "net.ipv6.conf.all.disable_ipv6=1"
Date	Tue, 06 Jun 2023 18:00:02 +0200
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Hi Dylan,

On Tue, Jun 06, 2023 at 05:19:38AM -0400, Dylan Morrison wrote:
> Package: src:linux
> Version: 6.0.8-1
> Severity: normal
> Tags: ipv6
> X-Debbugs-Cc: dizzy@domad.science

First a note on the version, 6.0.8-1 is not in testing, please update
to 6.1.27-1. 

> Dear Maintainer,
> 
> I am attempting to disable ipv6 entirely on this machine as it being enabled is causing multiple issues with long connection timeouts etc, and I do not have ipv6 support from my ISP nor do I use it locally. However, the generally given advice to set net.ipv6.conf.all.disable_ipv6 to 1 is having no effect, neither setting it in /etc/sysctl.conf nor using command line sysctl. Setting net.conf.ipv6.<adapter>.disable_ipv6 works, and is what I am currently doing for my primary network interface, but I would like ipv6 disabled globally.
> This appears to be a kernel issue afaict, I'm not 100% up on how the sysctl mechanism works, but yeah.

After updating to 6.1.27, can you elaborate how IPv6 not disabled is
observed? Note that reading net.ipv6.conf.all.disable_ipv6 and getting
1 is not an indicator of IPv6 beeing not disabled, cf.
https://www.kernel.org/doc/html/latest/networking/ip-sysctl.html?highlight=conf/all/disable_ipv6
.

What does 'ip add show' shows, and what does it show after executing
sysctl net.ipv6.conf.all.disable_ipv6=1 ?

ipv6 can as well entirely be disabled by using the disable_ipv6 kernel
parameter, cf. https://www.kernel.org/doc/html/latest/admin-guide/kernel-parameters.html?highlight=disable_ipv6=
that is e.g. adding ipv6.disable=1 to the kernel command line. Trough
grub2 you could add 

# cat /etc/default/grub.d/ipv6.cfg 
GRUB_CMDLINE_LINUX="$GRUB_CMDLINE_LINUX ipv6.disable_ipv6=1"

and run update-grub2.

I would like to understand what makes for you disabling it trough
net.ipv6.conf.all.disable_ipv6 not work.

Regards,
Salvatore

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Bug#1037138: linux-image-6.0.0-4-amd64: Linux kernel appears to not be respecting sysctl config value "net.ipv6.conf.all.disable_ipv6=1" Salvatore Bonaccorso <carnil@debian.org> - 2023-06-06 18:00 +0200

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