[clang][analyzer] PutenvStackArrayChecker: No warning from 'main' (llvm#93299)

Author: balazske

clang/docs/analyzer/checkers.rst

@@ -2858,6 +2858,16 @@ The check corresponds to CERT rule
     return putenv(env); // putenv function should not be called with stack-allocated string
   }
 
+There is one case where the checker can report a false positive. This is when
+the stack-allocated array is used at `putenv` in a function or code branch that
+does not return (calls `fork` or `exec` like function).
+
+Another special case is if the `putenv` is called from function `main`. Here
+the stack is deallocated at the end of the program and it should be no problem
+to use the stack-allocated string (a multi-threaded program may require more
+attention). The checker does not warn for cases when stack space of `main` is
+used at the `putenv` call.
+
 .. _alpha-security-ReturnPtrRange:
 
 alpha.security.ReturnPtrRange (C)

clang/lib/StaticAnalyzer/Checkers/PutenvStackArrayChecker.cpp

@@ -44,9 +44,14 @@ void PutenvStackArrayChecker::checkPostCall(const CallEvent &Call,
 
   SVal ArgV = Call.getArgSVal(0);
   const Expr *ArgExpr = Call.getArgExpr(0);
-  const MemSpaceRegion *MSR = ArgV.getAsRegion()->getMemorySpace();
 
-  if (!isa<StackSpaceRegion>(MSR))
+  const auto *SSR =
+      dyn_cast<StackSpaceRegion>(ArgV.getAsRegion()->getMemorySpace());
+  if (!SSR)
+    return;
+  const auto *StackFrameFuncD =
+      dyn_cast_or_null<FunctionDecl>(SSR->getStackFrame()->getDecl());
+  if (StackFrameFuncD && StackFrameFuncD->isMain())
     return;
 
   StringRef ErrorMsg = "The 'putenv' function should not be called with "

clang/test/Analysis/putenv-stack-array.c

@@ -45,6 +45,15 @@ int test_auto_var_subarray() {
   return putenv(env + 100); // expected-warning{{The 'putenv' function should not be called with}}
 }
 
+int f_test_auto_var_call(char *env) {
+  return putenv(env); // expected-warning{{The 'putenv' function should not be called with}}
+}
+
+int test_auto_var_call() {
+  char env[1024];
+  return f_test_auto_var_call(env);
+}
+
 int test_constant() {
   char *env = "TEST";
   return putenv(env); // no-warning: data is not on the stack
@@ -68,3 +77,14 @@ void test_auto_var_reset() {
   // become invalid.
   putenv((char *)"NAME=anothervalue");
 }
+
+void f_main(char *env) {
+  putenv(env); // no warning: string allocated in stack of 'main'
+}
+
+int main(int argc, char **argv) {
+  char env[] = "NAME=value";
+  putenv(env); // no warning: string allocated in stack of 'main'
+  f_main(env);
+  return 0;
+}