What were you trying to do that didn't work?

I create a sysctl.d config to overwrite certain network interface parameters such as rp_filter. However it seems the config at /run/sysctl.d/99-test.conf  gets ignored by systemd-sysctl but only if it is executed by the udev rule which should apply the right sysctl parameters for the new interface.

What is the impact of this issue to you?

It breaks podman routing as the sysctl we are trying to set are getting overridden.

https://issues.redhat.com/browse/RHEL-89477

Please provide the package NVR for which the bug is seen:

systemd-252-51.el9.x86_64

I also observed the same behavior on fedora with systemd-256

How reproducible is this bug?:

always

Steps to reproduce

mkdir /run/sysctl.d && echo "net/ipv4/conf/test/rp_filter = 2" >/run/sysctl.d/99-test.conf && ip link add test type dummy && echo 2 > /proc/sys/net/ipv4/conf/test/rp_filter && cat /proc/sys/net/ipv4/conf/test/rp_filter && sleep 1 && cat /proc/sys/net/ipv4/conf/test/rp_filter

To verify the file access we can check with bpftrace in another terminal which shows the systemd-syctl does not open the config file.

bpftrace -e 'tracepoint:syscalls:sys_enter_openat /strcontains(str(args.filename), "rp_filter") || strcontains(str(args.filename), "99-test")/ { printf("%s %s\n", comm, str(args.filename)); }' 

Expected results

2
2

Actual results

2
1

Note when I manually run /usr/lib/systemd/systemd-sysctl --prefix=/net/ipv4/conf/test from the cli the config file is read correctly and the right value is configured. So it seems related to it being executed by the udev rule.