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Data flow: Earlier pruning based on accessPathLimit #22320

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Data flow: Earlier pruning based on accessPathLimit #22320

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39 changes: 37 additions & 2 deletions shared/dataflow/codeql/dataflow/internal/DataFlowImpl.qll
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Original file line number Diff line number Diff line change
Expand Up @@ -561,6 +561,21 @@ module MakeImpl<LocationSig Location, InputSig<Location> Lang> {
)
}

pragma[nomagic]
private int getAnApLengthLowerBound(Ap ap) {
accessPathLimit() > 1 and // `accessPathLimit() <= 1` is already checked in stages 1 and 2
ap instanceof ApNil and
result = 0
or
exists(Content c, Ap tail |
ap = apCons(c, tail) and
fwdFlowConsCand(_, ap, c, _, tail) and
ap != tail and // no need to report a longer length
result = 1 + getAnApLengthLowerBound(tail) and
result <= accessPathLimit()
)
}

pragma[nomagic]
private predicate fwdFlow0(
Nd node, Cc cc, SummaryCtx summaryCtx, Typ t, Ap ap, ApApprox apa, TypOption stored
Expand Down Expand Up @@ -594,7 +609,10 @@ module MakeImpl<LocationSig Location, InputSig<Location> Lang> {
exists(Content c, Ap ap0 |
fwdFlowStore(_, _, ap0, _, c, t, stored, node, cc, summaryCtx) and
ap = apCons(c, ap0) and
apa = getApprox(ap)
apa = getApprox(ap) and
if accessPathLimit() > 1
then getAnApLengthLowerBound(ap0) < accessPathLimit()
else any()
)
or
// read
Expand Down Expand Up @@ -1320,6 +1338,20 @@ module MakeImpl<LocationSig Location, InputSig<Location> Lang> {
fwdFlow(node, _, _, _, ap, _)
}

pragma[nomagic]
private int getAnApLengthLowerBoundRev(Ap ap) {
accessPathLimit() > 1 and // `accessPathLimit() <= 1` is already checked in stages 1 and 2
ap instanceof ApNil and
result = 0
or
exists(Ap tail |
revFlowConsCand(ap, _, tail) and
ap != tail and // no need to report a longer length
result = 1 + getAnApLengthLowerBoundRev(tail) and
result <= accessPathLimit()
)
}

pragma[nomagic]
private predicate revFlow0(Nd node, ReturnCtx returnCtx, ApOption returnAp, Ap ap) {
fwdFlow(node, _, any(SummaryCtx sinkCtx | sinkCtx.isASinkCtx()), _, ap, _) and
Expand Down Expand Up @@ -1356,7 +1388,10 @@ module MakeImpl<LocationSig Location, InputSig<Location> Lang> {
// read
exists(Nd mid, Ap ap0 |
revFlow(mid, returnCtx, returnAp, ap0) and
readStepFwd(node, ap, _, mid, ap0)
readStepFwd(node, ap, _, mid, ap0) and
if accessPathLimit() > 1
then getAnApLengthLowerBoundRev(ap0) < accessPathLimit()
else any()
)
or
// flow into a callable
Expand Down
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