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C++: Cleanup ScanfChecks.qll #20400

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Merged
merged 2 commits into from
Sep 10, 2025
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C++: Cleanup ScanfChecks.qll #20400

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d097946
C++: No need for this additional case.
MathiasVP Sep 10, 2025
72d7223
C++: Small drive by cleanup. Delete unnecessary nested 'exists'.
MathiasVP Sep 10, 2025
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34 changes: 14 additions & 20 deletions cpp/ql/src/Critical/ScanfChecks.qll
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Original file line number Diff line number Diff line change
Expand Up @@ -4,13 +4,9 @@ private import semmle.code.cpp.controlflow.IRGuards
private import semmle.code.cpp.ir.ValueNumbering

private predicate exprInBooleanContext(Expr e) {
exists(IRGuardCondition gc |
exists(Instruction i |
i.getUnconvertedResultExpression() = e and
gc.comparesEq(valueNumber(i).getAUse(), 0, _, _)
)
or
gc.getUnconvertedResultExpression() = e
Comment on lines -12 to -13
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@jketema jketema Sep 10, 2025

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Why can this be removed?

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@MathiasVP MathiasVP Sep 10, 2025

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Oh, yes. Sorry I should have made that clear.

This is a left-over from back when we didn't have guard conditions for unary conditions. When we only had the binary guard conditions we did not have a guard condition logic for stuff like if(x) { } and if(!x) { }. So the workaround was to check whether the guard condition was equal to the expression.

I switched the ScanfChecks library to use the unary guard condition predicate in decede5, but I forgot to delete this disjunct.

exists(IRGuardCondition gc, Instruction i |
i.getUnconvertedResultExpression() = e and
gc.comparesEq(valueNumber(i).getAUse(), 0, _, _)
)
}

Expand All @@ -36,20 +32,18 @@ private string getEofValue() {
* Holds if the value of `call` has been checked to not equal `EOF`.
*/
private predicate checkedForEof(ScanfFunctionCall call) {
exists(IRGuardCondition gc |
exists(CallInstruction i | i.getUnconvertedResultExpression() = call |
exists(int val | gc.comparesEq(valueNumber(i).getAUse(), val, _, _) |
// call == EOF
val = getEofValue().toInt()
or
// call == [any positive number]
val > 0
)
exists(IRGuardCondition gc, CallInstruction i | i.getUnconvertedResultExpression() = call |
exists(int val | gc.comparesEq(valueNumber(i).getAUse(), val, _, _) |
// call == EOF
val = getEofValue().toInt()
or
exists(int val | gc.comparesLt(valueNumber(i).getAUse(), val, true, _) |
// call < [any non-negative number] (EOF is guaranteed to be negative)
val >= 0
)
// call == [any positive number]
val > 0
)
or
exists(int val | gc.comparesLt(valueNumber(i).getAUse(), val, true, _) |
// call < [any non-negative number] (EOF is guaranteed to be negative)
val >= 0
)
)
}
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