C++: Improve hasUpperBoundsCheck#3062
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jbj
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Mar 16, 2020
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I'm happy with this, but the qlformat check is failing.
| @@ -139,10 +149,10 @@ private predicate writesVariable(StoreInstruction store, Variable var) { | |||
| // previously suppressed by this predicate by coincidence. | |||
| private predicate hasUpperBoundsCheck(Variable var) { | |||
| exists(RelationalOperation oper, VariableAccess access | | |||
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Would you go so far as to change RelationalOperation to ComparisonOperation? I think we've seen some code recently that took a size from the network, verified that it was equal to some constant, and then allocated that size of memory.
It doesn't have to be in this PR.
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I'll look into this as a follow-up (I think I remember seeing that code).
jbj
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Apr 7, 2020
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Change
hasUpperBoundsCheckso that more kinds of bounds are accepted, leading to fewer false positives from TaintedAllocationSize.ql (see #2762 and #3016). There are still some accuracy issues around the 'multiplication by a sizeof' part of this query, but I'm not happy with my solution to that yet, so further changes will come as a follow-up.Note that in the long run we intend to replace
hasUpperBoundsCheckwith a more robust mechanism (at the moment for example, we don't care where the upper bounds check occurs, it might occur after the allocation has been made).