Ensure overlay kernel module is not available

How it is checked

Audit method: Shell command

m=overlay; found=$(find /lib/modules/$(uname -r)/kernel /usr/lib/modules/$(uname -r)/kernel -path "*/overlay*" 2>/dev/null | head -n1); if [ -z "$found" ]; then echo compliant; exit 0; fi; lsmod | awk '{print $1}' | grep -Fxq -- "${m//-/_}" && { echo "$m is loaded"; exit 0; }; cfg=$(modprobe --showconfig 2>/dev/null); printf '%s\n' "$cfg" | grep -Pq -- "^\h*blacklist\h+${m//-/_}\b" || { echo "$m is not blacklisted"; exit 0; }; printf '%s\n' "$cfg" | grep -Pq -- "^\h*install\h+${m//-/_}\h+(/usr)?/bin/(true|false)\b" || { echo "$m install is not disabled"; exit 0; }; echo compliant

Expected output

compliant

How it is fixed

Fix method: Guidance or infrastructure patch

Unload and disable the overlay kernel module. 1. Run the following commands to unload the overlay kernel module: # modprobe -r overlay 2>/dev/null # rmmod overlay 2>/dev/null 2. Perform the following to disable the overlay kernel module: Create a file ending in .conf with install overlay /bin/false in the /etc/modprobe.d/ directory Example: # printf '%s\n' "" "install overlay /bin/false" >> /etc/modprobe.d/60- overlay.conf Create a file ending in .conf with blacklist overlay in the /etc/modprobe.d/ directory Example: # printf '%s\n' "" "blacklist overlay" >> /etc/modprobe.d/60-overlay.conf

Check this host

Run this on a machine you are allowed to audit. The scan is read-only.

tmaegis scan --target linux --level 2