dsize keyword improvements
Today, dsize is limited to detect if a payload size is smaller, equal or larger than a single value.
In order to improve abnormal packets detection, signatures should be able to:
- Detect if dsize is different than a specified value.
- Allow multiple dsizes in the same signature.
For example, I've got 2 use-cases from real world.
I've got an industrial protocol that uses the same payload size in every packet, let's say 100B. Today, I've got to write 2 rules, one with "dsize<100;" and a second one with "dsize>100;" as multiple dsizes are not allowed in the same signature.
It would be nice to write a single rule with dsize:!100;
Another protocol uses only 2 payload sizes, depending on the packet type, let's use 100B and 150B. I cannot detect the full range of anomaly with the current implementation.
The improvement should allow to write: "dsize:!100; dsize:!150;" or "dsize:![100,150];" in the signature.