Public bug reported:
In 22.04, systemd ships the following globbed sysctls:
$ grep -r -F '*' /usr/lib/sysctl.d /etc/sysctl.*
/usr/lib/sysctl.d/50-default.conf:net.ipv4.conf.*.rp_filter = 2
/usr/lib/sysctl.d/50-default.conf:net.ipv4.conf.*.accept_source_route = 0
/usr/lib/sysctl.d/50-default.conf:net.ipv4.conf.*.promote_secondaries = 1
This seems to break linux's built-in .defaults sysctls. For instance,
`net.ipv4.conf.default.rp_filter` is ineffective given the above.
According to sysctl.d(5), they're applied /individually/ when interfaces show
up:
> The settings configured with sysctl.d files will be applied early on boot.
> The network interface-specific options will also be applied individually for
> each network interface as it shows up in the system. (More specifically,
> net.ipv4.conf.*, net.ipv6.conf.*, net.ipv4.neigh.* and net.ipv6.neigh.*).
That means something (networkd?) applies
`net.ipv4.conf.newif.rp_filter=2` when newif appears. Since that's
applied to an individual interface, it overrides
`net.ipv4.conf.default.rp_filter=0` that I've set. That pretty
surprising.
It isn't clear from sysctl.d(5) how to disable this. With some
experimentation, I've come up with:
-net.ipv4.conf.*.rp_filter
net.ipv4.conf.all.rp_filter = 0
net.ipv4.conf.default.rp_filter = 0
But I'm not sure that first line is valid. sysctl.d(5) doesn't document
this case.
Perhaps the systemd package should not ship globbed sysctls in the
above-documented network subtrees - are there use cases not covered by
the .defaults sysctls?
I haven't checked if later packages continue to ship the above config.
** Affects: systemd (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/2065439
Title:
default globbed sysctls override linux defaults
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