[clang] [analyzer] Fix crash in Stream checker when using void pointers (PR #97199)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang-static-analyzer-1

Author: Balazs Benics (steakhal)

<details>
<summary>Changes</summary>

We can get zero type size (thus div by zero crash) if the region is for a 'void*' pointer.
In this patch, let's just override the void type with a char type to avoid the crash.

Fixes
https://github.com/llvm/llvm-project/pull/93408#issuecomment-2189766510

---
Full diff: https://github.com/llvm/llvm-project/pull/97199.diff


2 Files Affected:

- (modified) clang/lib/StaticAnalyzer/Checkers/StreamChecker.cpp (+25-14) 
- (modified) clang/test/Analysis/stream.c (+13) 


``````````diff
diff --git a/clang/lib/StaticAnalyzer/Checkers/StreamChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/StreamChecker.cpp
index 9aee7f952ad2d..0d1d50d19f4c4 100644
--- a/clang/lib/StaticAnalyzer/Checkers/StreamChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/StreamChecker.cpp
@@ -1034,16 +1034,19 @@ void StreamChecker::preWrite(const FnDescription *Desc, const CallEvent &Call,
   C.addTransition(State);
 }
 
-static std::optional<QualType> getPointeeType(const MemRegion *R) {
+static QualType getPointeeType(const MemRegion *R) {
   if (!R)
-    return std::nullopt;
-  if (const auto *ER = dyn_cast<ElementRegion>(R))
-    return ER->getElementType();
-  if (const auto *TR = dyn_cast<TypedValueRegion>(R))
-    return TR->getValueType();
-  if (const auto *SR = dyn_cast<SymbolicRegion>(R))
-    return SR->getPointeeStaticType();
-  return std::nullopt;
+    return {};
+  QualType Ty = [R] {
+    if (const auto *ER = dyn_cast<ElementRegion>(R))
+      return ER->getElementType();
+    if (const auto *TR = dyn_cast<TypedValueRegion>(R))
+      return TR->getValueType();
+    if (const auto *SR = dyn_cast<SymbolicRegion>(R))
+      return SR->getPointeeStaticType();
+    return QualType{};
+  }();
+  return !Ty.isNull() ? Ty->getCanonicalTypeUnqualified() : QualType{};
 }
 
 static std::optional<NonLoc> getStartIndex(SValBuilder &SVB,
@@ -1073,7 +1076,16 @@ tryToInvalidateFReadBufferByElements(ProgramStateRef State, CheckerContext &C,
   const auto *Buffer =
       dyn_cast_or_null<SubRegion>(Call.getArgSVal(0).getAsRegion());
 
-  std::optional<QualType> ElemTy = getPointeeType(Buffer);
+  const ASTContext &Ctx = C.getASTContext();
+
+  QualType ElemTy = getPointeeType(Buffer);
+
+  // Consider pointer to void as a pointer to char buffer such that it has a
+  // non-zero type size.
+  if (!ElemTy.isNull() && ElemTy == Ctx.VoidTy) {
+    ElemTy = Ctx.CharTy;
+  }
+
   std::optional<SVal> StartElementIndex =
       getStartIndex(C.getSValBuilder(), Buffer);
 
@@ -1086,10 +1098,9 @@ tryToInvalidateFReadBufferByElements(ProgramStateRef State, CheckerContext &C,
   std::optional<int64_t> StartIndexVal =
       getKnownValue(State, StartElementIndex.value_or(UnknownVal()));
 
-  if (ElemTy && CountVal && Size && StartIndexVal) {
+  if (!ElemTy.isNull() && CountVal && Size && StartIndexVal) {
     int64_t NumBytesRead = Size.value() * CountVal.value();
-    int64_t ElemSizeInChars =
-        C.getASTContext().getTypeSizeInChars(*ElemTy).getQuantity();
+    int64_t ElemSizeInChars = Ctx.getTypeSizeInChars(ElemTy).getQuantity();
     bool IncompleteLastElement = (NumBytesRead % ElemSizeInChars) != 0;
     int64_t NumCompleteOrIncompleteElementsRead =
         NumBytesRead / ElemSizeInChars + IncompleteLastElement;
@@ -1097,7 +1108,7 @@ tryToInvalidateFReadBufferByElements(ProgramStateRef State, CheckerContext &C,
     constexpr int MaxInvalidatedElementsLimit = 64;
     if (NumCompleteOrIncompleteElementsRead <= MaxInvalidatedElementsLimit) {
       return escapeByStartIndexAndCount(State, Call, C.blockCount(), Buffer,
-                                        *ElemTy, *StartIndexVal,
+                                        ElemTy, *StartIndexVal,
                                         NumCompleteOrIncompleteElementsRead);
     }
   }
diff --git a/clang/test/Analysis/stream.c b/clang/test/Analysis/stream.c
index db03d90cd8af4..0869b1b325172 100644
--- a/clang/test/Analysis/stream.c
+++ b/clang/test/Analysis/stream.c
@@ -453,3 +453,16 @@ void getline_buffer_size_negative() {
   free(buffer);
   fclose(file);
 }
+
+void gh_93408_regression(void *buffer) {
+  FILE *f = fopen("/tmp/foo.txt", "r");
+  fread(buffer, 1, 1, f); // expected-warning {{Stream pointer might be NULL}} no-crash: void is treated as char.
+  fclose(f);
+}
+
+typedef void VOID;
+void gh_93408_regression_typedef(VOID *buffer) {
+  FILE *f = fopen("/tmp/foo.txt", "r");
+  fread(buffer, 1, 1, f); // expected-warning {{Stream pointer might be NULL}} no-crash: VOID is treated as char.
+  fclose(f);
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/97199