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Ruby/Python: Clear call contexts after jump steps in type tracking #8317

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Mar 7, 2022
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Ruby/Python: Clear call contexts after jump steps in type tracking #8317

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Ruby: Clear call contexts after jump steps in type tracking
hvitved Mar 3, 2022
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hvitved Mar 3, 2022
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hvitved Mar 3, 2022
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14 changes: 13 additions & 1 deletion python/ql/lib/semmle/python/dataflow/new/internal/TypeTracker.qll
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Original file line number Diff line number Diff line change
Expand Up @@ -34,7 +34,8 @@ private module Cached {
CallStep() or
ReturnStep() or
StoreStep(ContentName content) or
LoadStep(ContentName content)
LoadStep(ContentName content) or
JumpStep()

/** Gets the summary resulting from appending `step` to type-tracking summary `tt`. */
cached
Expand All @@ -49,6 +50,9 @@ private module Cached {
step = LoadStep(content) and result = MkTypeTracker(hasCall, "")
or
exists(string p | step = StoreStep(p) and content = "" and result = MkTypeTracker(hasCall, p))
or
step = JumpStep() and
result = MkTypeTracker(false, content)
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Looking at the JavaScript implementation of TypeTracker.append I see that none of the steps ever clear the hasCall property and vice-versa for hasReturn in TypeBackTracker.prepend. @asgerf , what do you think?

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None of our type-tracking steps are jump-steps. No fundamental reason not to have them, we just haven't added them.

Note we handle captured variables differently; they are not modelled as jump steps (which is too imprecise for JS code). Also, when writing a type-tracking predicate, you may choose to manually reset the calling context using t.start() (I'm working on a doc describing the importance of this in more detail). Perhaps this is why it never seemed important for JS.

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@asgerf Thanks for the explanation. Just wanted to be sure that there wasn't a fundamental reason why resetting the hasCall/hasReturn flags would be bad.

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@hvitved hvitved Mar 3, 2022 •
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Also, when writing a type-tracking predicate, you may choose to manually reset the calling context using t.start()

Doesn't that also clear whether or not data is stored in a property?

)
}

Expand All @@ -67,6 +71,9 @@ private module Cached {
)
or
step = StoreStep(content) and result = MkTypeBackTracker(hasReturn, "")
or
step = JumpStep() and
result = MkTypeBackTracker(false, content)
)
}

Expand Down Expand Up @@ -110,12 +117,17 @@ class StepSummary extends TStepSummary {
exists(string content | this = StoreStep(content) | result = "store " + content)
or
exists(string content | this = LoadStep(content) | result = "load " + content)
or
this instanceof JumpStep and result = "jump"
}
}

pragma[noinline]
private predicate smallstepNoCall(Node nodeFrom, TypeTrackingNode nodeTo, StepSummary summary) {
jumpStep(nodeFrom, nodeTo) and
summary = JumpStep()
or
levelStep(nodeFrom, nodeTo) and
summary = LevelStep()
or
exists(string content |
Expand Down
3 changes: 3 additions & 0 deletions python/ql/lib/semmle/python/dataflow/new/internal/TypeTrackerSpecific.qll
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Expand Up @@ -14,6 +14,9 @@ predicate simpleLocalFlowStep = DataFlowPrivate::simpleLocalFlowStep/2;

predicate jumpStep = DataFlowPrivate::jumpStep/2;

/** Holds if there is a level step from `pred` to `succ`. */
predicate levelStep(Node pred, Node succ) { none() }

/**
* Gets the name of a possible piece of content. For Python, this is currently only attribute names,
* using the name of the attribute for the corresponding content.
Expand Down
14 changes: 13 additions & 1 deletion ruby/ql/lib/codeql/ruby/typetracking/TypeTracker.qll
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Original file line number Diff line number Diff line change
Expand Up @@ -34,7 +34,8 @@ private module Cached {
CallStep() or
ReturnStep() or
StoreStep(ContentName content) or
LoadStep(ContentName content)
LoadStep(ContentName content) or
JumpStep()

/** Gets the summary resulting from appending `step` to type-tracking summary `tt`. */
cached
Expand All @@ -49,6 +50,9 @@ private module Cached {
step = LoadStep(content) and result = MkTypeTracker(hasCall, "")
or
exists(string p | step = StoreStep(p) and content = "" and result = MkTypeTracker(hasCall, p))
or
step = JumpStep() and
result = MkTypeTracker(false, content)
)
}

Expand All @@ -67,6 +71,9 @@ private module Cached {
)
or
step = StoreStep(content) and result = MkTypeBackTracker(hasReturn, "")
or
step = JumpStep() and
result = MkTypeBackTracker(false, content)
)
}

Expand Down Expand Up @@ -110,12 +117,17 @@ class StepSummary extends TStepSummary {
exists(string content | this = StoreStep(content) | result = "store " + content)
or
exists(string content | this = LoadStep(content) | result = "load " + content)
or
this instanceof JumpStep and result = "jump"
}
}

pragma[noinline]
private predicate smallstepNoCall(Node nodeFrom, TypeTrackingNode nodeTo, StepSummary summary) {
jumpStep(nodeFrom, nodeTo) and
summary = JumpStep()
or
levelStep(nodeFrom, nodeTo) and
summary = LevelStep()
or
exists(string content |
Expand Down
3 changes: 3 additions & 0 deletions ruby/ql/lib/codeql/ruby/typetracking/TypeTrackerSpecific.qll
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Original file line number Diff line number Diff line change
Expand Up @@ -15,6 +15,9 @@ predicate simpleLocalFlowStep = DataFlowPrivate::localFlowStepTypeTracker/2;

predicate jumpStep = DataFlowPrivate::jumpStep/2;

/** Holds if there is a level step from `pred` to `succ`. */
predicate levelStep(Node pred, Node succ) { none() }

/**
* Gets the name of a possible piece of content. This will usually include things like
*
Expand Down