Provenance information records the source and ownership history of an object. We study the problem of provenance tracking in concurrent programs, in which several principals execute concurrent processes and exchange messages over unbounded but unordered channels. The provenance of a message, roughly, is a function of the sequence of principals that have transmitted the message in the past. The provenance verification problem is to statically decide, given a message passing program and a set of allowed provenances, whether the provenance of all messages in all possible program executions, belongs to the allowed set. We formalize the provenance verification problem abstractly in terms of well-structured provenance domains, and show a general decidability result for it. In particular, we show that if the provenance of a message is a sequence of principals who have sent the message, and a provenance query asks if the provenance lies in a regular set, the problem is decidable and EXPSPACE-complete. While the theoretical complexity is high, we show an implementation of our technique that performs efficiently on a set of Javascript examples tracking provenances in Firefox extensions. Our experiments show that many browser extensions store and transmit user information although the user sets the browser to the private mode.
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