Qiskit / qiskit / 27433757677

88%

Build Type

push

github

Committed by web-flow

Commit Message

Fix stack-overflow segfault in OpenQASM 2 expression parsers (#16421)

* Fix stack-overflow segfault in OpenQASM 2 expression parsers

The current recursive implementation of the operator-precedence
expression parsers is susceptible to overflowing the stack on
excessively deep expressions.  The simplest way to trigger this is to
enter an arbitrary number of parentheses.

This patch puts a simple recursion-depth limit on the expression parser
to safely error out before it comes close to the stack depth.  We use
`sys.getrecursionlimit` on input simply as a compromise between not
wanting to define new keyword arguments in bugfix patches and still
wanting to allow some amount of control over the limit.

Future patches could consider replacing the recursive components of the
expression parser with iterative state-tracking parsing.  The outer
recursive-descent parser that handles the rest of the OpenQASM 2 grammar
has a bounded recursion depth by nature of the grammar it is parsing; it
is only the expression subparser that can reach arbitrary depths.

* Lower recursion limit

Coverage Stats

28 of 28 new or added lines in 5 files covered. (100.0%)

25 existing lines in 3 files now uncovered.

110770 of 126630 relevant lines covered (87.48%)

964843.82 hits per line