The iptables mark field is 32 bits wide, which is 4 bytes and so 8 hex characters. Fix the fwmark validation to allow 8 characters in the hex string. Fixes: #5098 Suggested-by: Robert <32970961+differentblue@users.noreply.github.com> Signed-off-by: Jo-Philipp Wich <jo@mein.io> (cherry picked from commit bc1015f7db57506b2468846f79dbd5bfe0dbea7a)