comparison mercurial/linelog.py @ 38935:27a54096c92e

linelog: fix infinite loop vulnerability

Checking `len(lines)` is not a great way of detecting infinite loops, as
demonstrated in the added test. Therefore check instruction count instead.

The original C implementation does not have this problem. There are a few
other places where the C implementation enforces more strictly, like
`a1 <= a2`, `b1 <= b2`, `rev > 0`. But they are optional.

Test Plan:
Add a test. The old code forces the test to time out.

Differential Revision: https://phab.mercurial-scm.org/D4151

38934:35180ade80c1

            self._maxrev = rev

    def annotate(self, rev):
        pc = 1
        lines = []
        # Sanity check: if len(lines) is longer than len(program), we
        # hit an infinite loop in the linelog program somehow and we
        # should stop.
        while pc is not None and len(lines) < len(self._program):
            inst = self._program[pc]
            lastpc = pc
            pc = inst.execute(rev, pc, lines.append)
        if pc is not None:
            raise LineLogError(
                'Probably hit an infinite loop in linelog. Program:\n' +
                self.debugstr())
        ar = annotateresult(rev, lines, lastpc)

38935:27a54096c92e

            self._maxrev = rev

    def annotate(self, rev):
        pc = 1
        lines = []
        executed = 0
        # Sanity check: if instructions executed exceeds len(program), we
        # hit an infinite loop in the linelog program somehow and we
        # should stop.
        while pc is not None and executed < len(self._program):
            inst = self._program[pc]
            lastpc = pc
            pc = inst.execute(rev, pc, lines.append)
            executed += 1
        if pc is not None:
            raise LineLogError(
                'Probably hit an infinite loop in linelog. Program:\n' +
                self.debugstr())
        ar = annotateresult(rev, lines, lastpc)