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C++: Use range analysis at the sink to exclude trivial FPs.

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Mathias Vorreiter Pedersen
2024-10-07 17:15:22 +01:00
parent c3d9ea1820
commit a2cdb9c173
1 changed files with 14 additions and 2 deletions
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16
cpp/ql/src/Security/CWE/CWE-129/ImproperArrayIndexValidation.ql
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@@ -16,7 +16,7 @@ import cpp
import semmle.code.cpp.controlflow.IRGuards
import semmle.code.cpp.security.FlowSources as FS
import semmle.code.cpp.dataflow.new.TaintTracking
import semmle.code.cpp.rangeanalysis.RangeAnalysisUtils
import semmle.code.cpp.rangeanalysis.SimpleRangeAnalysis
import ImproperArrayIndexValidation::PathGraph
predicate isFlowSource(FS::FlowSource source, string sourceType) {
@@ -39,6 +39,17 @@ predicate guardChecks(IRGuardCondition g, Expr e, boolean branch) {
)
}
/**
* Holds if `arrayExpr` accesses an `ArrayType` with a constant size `N`, and
* the value of `offsetExpr` is known to be smaller than `N`.
*/
predicate offsetIsAlwaysInBounds(ArrayExpr arrayExpr, VariableAccess offsetExpr) {
exists(ArrayType arrayType |
arrayType = arrayExpr.getArrayBase().getUnspecifiedType() and
arrayType.getArraySize() > upperBound(offsetExpr.getFullyConverted())
)
}
module ImproperArrayIndexValidationConfig implements DataFlow::ConfigSig {
predicate isSource(DataFlow::Node source) { isFlowSource(source, _) }
@@ -51,7 +62,8 @@ module ImproperArrayIndexValidationConfig implements DataFlow::ConfigSig {
predicate isSink(DataFlow::Node sink) {
exists(ArrayExpr arrayExpr, VariableAccess offsetExpr |
offsetExpr = arrayExpr.getArrayOffset() and
sink.asExpr() = offsetExpr
sink.asExpr() = offsetExpr and
not offsetIsAlwaysInBounds(arrayExpr, offsetExpr)
)
}
}