CVE-2024-54683

In the Linux kernel, the following vulnerability has been resolved:

netfilter: IDLETIMER: Fix for possible ABBA deadlock

Deletion of the last rule referencing a given idletimer may happen at the same time as a read of its file in sysfs:

| ====================================================== | WARNING: possible circular locking dependency detected

A simple reproducer is:

| #!/bin/bash | | while true; do | iptables -A INPUT -i foo -j IDLETIMER --timeout 10 --label "testme" | iptables -D INPUT -i foo -j IDLETIMER --timeout 10 --label "testme" | done & | while true; do | cat /sys/class/xt_idletimer/timers/testme >/dev/null | done

Avoid this by freeing list_mutex right after deleting the element from the list, then continuing with the teardown.