[PATCH] D30909: [Analyzer] Finish taint propagation to derived symbols of tainted regions

[Vlad Tsyrklevich via Phabricator via cfe-commits]

vlad.tsyrklevich added inline comments.


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Comment at: lib/StaticAnalyzer/Checkers/GenericTaintChecker.cpp:494
+  SymbolManager &SM = C.getSymbolManager();
+  return SM.getDerivedSymbol(Sym, LCV.getRegion());
 }
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NoQ wrote:
> I'd think about this a bit more and come back.
> 
> I need to understand how come that constructing a symbol manually is the right thing to do; that doesn't happen very often, but it seems correct here.
Indeed it is odd. The best justification I could come up with: LCVs are meant to be optimizations, their 'purpose' is to expose an SVal that hides SymbolRef values so that we can have a split store. We don't have to copy all of a compound values SymbolRef mappings because LCVs are kept distinct. Hence to set/query/constrain region values you use SVals so that RegionStore can differentiate between LCVs and SymbolRef backed SVals for the two different stores it contains.

The taint interface however requires you taint a SymbolRef, not an SVal. If we wanted, instead of doing this logic here, we could change getPointedToSymbol() to return an SVal and update usages of it accordingly since that value is only passed on to ProgramState.isTainted()/ProgramState.addTaint() anyway. Then we could update addTaint/isTainted to perform this logic, hiding it from the checker.

This still requires manually constructing a symbol, now it's just performed in the analyzer instead of in a checker. Not sure if that addresses the issue you were considering, but the idea that we need to 'undo' the LCV optimization hiding the SymbolRef to have a value to taint seems somewhat convincing to me. What do you think?


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Comment at: test/Analysis/taint-generic.c:210
+  read(sock, &tainted.st, sizeof(tainted.st));
+  __builtin_memcpy(buffer, tainted.buf, tainted.st[0].length); // expected-warning {{Untrusted data is used to specify the buffer size}}
 }
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NoQ wrote:
> Are we already supporting the case when we're tainting some elements of an array but not all of them, and this works as expected? Could we add such tests (regardless of whether we already handle them)?
It does work in that case. If you taint element X of region Y the current logic will be conservative and only mark element X as tainted, not X-i or X+i. This is also true for element 0, so if a programmer passes &array[0] but reads sizeof(array) bytes it will not correctly mark that. This is also a short coming of the invalidation code so I don't think there's much to do until there's more general support for dealing with region extents.


https://reviews.llvm.org/D30909