private: Policy.PolicyFromExtPolicy modifies existing policy.

[tzaeschke]

While porting the path policy language to JPAN, I came across this code in private/path/pathpol/policy.go:

scion/private/path/pathpol/policy.go

Line 97 in 6e7f052

policy := extPolicy.Policy

The first line in the methods takes the *Policy from the extPolicy and then (unless it is nil) modifies and returns it.
However, the comment on the function states that a new policy would be created and returned.
Moreover, this appears to be the only function in this module that allows modifying existing policies.

I suspect the first line is wrong and should instead copy the policy object.

Is that a bug?

[jiceatscion]

I agree with you that it's pretty suspicious. It almost looks like extPolicy.Policy used to be a value and was changed to a pointer without sufficient consideration.