Foxhound: Don't add duplicate taint operations

[tmbrbr]

Don't add a new TaintNode if the operation is the same (i.e. same Operation, Arguments and Location) as the previous operation. This way, we only add a single operation in e.g. a for loop.

[leeN]

The changes generally look perfectly fine; I'm wondering whether we might lose information that could be interesting.

If I understand it correctly, if we repeatedly perform the same operation, we won't add this anymore.

Say, and this is somewhat contrived, we have code like this:

let foo = location.hash;
for(int i = 0; i < 3; i++) {
  foo = decodeURIComponent(foo);
}

If, for example, we do not do URI encoding, the taint flow only has 1 decode operation. It might be possible to encode several times to end up with an XSS payload after this loop, which we would not be able to find anymore, right?

[tmbrbr]

Good catch, perhaps we can add a counter to the taint operations to keep track of this.