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JS: Don't compute big string concatenations in Expr.qll #4624

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Nov 6, 2020
Merged

JS: Don't compute big string concatenations in Expr.qll #4624

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19 changes: 14 additions & 5 deletions javascript/ql/src/semmle/javascript/Expr.qll
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Original file line number Diff line number Diff line change
Expand Up @@ -1603,17 +1603,26 @@ private predicate hasAllConstantLeafs(AddExpr add) {
private string getConcatenatedString(Expr add) {
result = getConcatenatedString(add.getUnderlyingValue())
or
not add = getAnAddOperand(any(AddExpr parent | hasAllConstantLeafs(parent))) and
hasAllConstantLeafs(add) and
result =
strictconcat(Expr leaf |
leaf = getAnAddOperand*(add)
leaf = getAnAddOperand*(add.(SmallConcatRoot))
|
getConstantString(leaf)
order by
leaf.getLocation().getStartLine(), leaf.getLocation().getStartColumn()
) and
result.length() < 1000 * 1000
)
}

/**
* An expr that is the root of a string concatenation of constant parts,
* and the length of the resulting concatenation is less than 1 million chars.
*/
private class SmallConcatRoot extends Expr {
SmallConcatRoot() {
not this = getAnAddOperand(any(AddExpr parent | hasAllConstantLeafs(parent))) and
hasAllConstantLeafs(this) and
sum(Expr leaf | leaf = getAnAddOperand*(this) | getConstantString(leaf).length()) < 1000 * 1000
}
}

/**
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