TCP/IP connection stuck when called from UDEV rule

[Paskin]

It seems that in Eoan there is a lock/any other issue preventing particular system calls to be executed by the triggered action handler. I have an action executing wget when USB-serial adapter is plugged:

SUBSYSTEM=="tty", ACTION=="add", ATTRS{idVendor}=="1a86", ATTRS{idProduct}=="7523", MODE="0666", RUN+="/usr/bin/wget -v --method=POST http://127.0.0.1:4000/udev_trigger/add"
This action works perfectly in a prior versions - but in Eoan Ermine it hangs for ~30s and fails on a timeout. Analysis with strace shows that execution is stuck on connect() syscall - until it returns with ETIMEDOUT.

Same Wget command, being run from a command line, works perfectly.

The issue doesn't seem to be related to a particular IP (localhost/remote) and/or the status of a listener process - execution hangs also when listener is not running and port is free.

[Nick Rosbrook (enr0n)]

udev restricts this sort of thing for security reasons, so this is working as expected.

[Paskin (khalatov)]

Could you refer to some documentation on this restriction (especially - what actions are allowed/restricted)?

In addition - what was the reason of DROP behaviour? All known to me system restrictions behave as REJECT - i.e. restricted action gets an immediate result instead on being stuck until the timeout expires...

[Nick Rosbrook (enr0n)]

From the udev man page:

"Note that running programs that access the network or mount/unmount filesystems is not allowed inside of udev rules, due to the default sandbox that is enforced on systemd-udevd.service."

I have not tested or looked into the specifics of the implementation to be able to answer your second question.