[-Wunsafe-buffer-usage] Warning Libc functions (llvm#101583)

[-Wunsafe-buffer-usage] Add warn on unsafe calls to libc functions

Warning about calls to libc functions involving buffer access.  Warned
functions are hardcoded by names.

(rdar://117182250)

clang/include/clang/Analysis/Analyses/UnsafeBufferUsage.h

@@ -15,6 +15,7 @@
 #define LLVM_CLANG_ANALYSIS_ANALYSES_UNSAFEBUFFERUSAGE_H
 
 #include "clang/AST/Decl.h"
+#include "clang/AST/Expr.h"
 #include "clang/AST/Stmt.h"
 #include "clang/Basic/SourceLocation.h"
 #include "llvm/Support/Debug.h"
@@ -106,6 +107,20 @@ class UnsafeBufferUsageHandler {
   virtual void handleUnsafeOperation(const Stmt *Operation,
                                      bool IsRelatedToDecl, ASTContext &Ctx) = 0;
 
+  /// Invoked when a call to an unsafe libc function is found.
+  /// \param PrintfInfo
+  ///  is 0 if the callee function is not a member of the printf family;
+  ///  is 1 if the callee is `sprintf`;
+  ///  is 2 if arguments of the call have `__size_by` relation but are not in a
+  ///  safe pattern;
+  ///  is 3 if string arguments do not guarantee null-termination
+  ///  is 4 if the callee takes va_list
+  /// \param UnsafeArg one of the actual arguments that is unsafe, non-null
+  /// only when `2 <= PrintfInfo <= 3`
+  virtual void handleUnsafeLibcCall(const CallExpr *Call, unsigned PrintfInfo,
+                                    ASTContext &Ctx,
+                                    const Expr *UnsafeArg = nullptr) = 0;
+
   /// Invoked when an unsafe operation with a std container is found.
   virtual void handleUnsafeOperationInContainer(const Stmt *Operation,
                                                 bool IsRelatedToDecl,

clang/include/clang/Analysis/Analyses/UnsafeBufferUsageGadgets.def

@@ -38,6 +38,7 @@ WARNING_GADGET(PointerArithmetic)
 WARNING_GADGET(UnsafeBufferUsageAttr)
 WARNING_GADGET(UnsafeBufferUsageCtorAttr)
 WARNING_GADGET(DataInvocation)
+WARNING_GADGET(UnsafeLibcFunctionCall)
 WARNING_CONTAINER_GADGET(SpanTwoParamConstructor) // Uses of `std::span(arg0, arg1)`
 FIXABLE_GADGET(ULCArraySubscript)          // `DRE[any]` in an Unspecified Lvalue Context
 FIXABLE_GADGET(DerefSimplePtrArithFixable)

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -12412,6 +12412,13 @@ def warn_unsafe_buffer_operation : Warning<
   "unsafe buffer access|function introduces unsafe buffer manipulation|unsafe invocation of span::data|"
   "field %1 prone to unsafe buffer manipulation}0">,
   InGroup<UnsafeBufferUsage>, DefaultIgnore;
+def warn_unsafe_buffer_libc_call : Warning<
+  "function %0 is unsafe">,
+  InGroup<UnsafeBufferUsage>, DefaultIgnore;
+def note_unsafe_buffer_printf_call : Note<
+  "%select{|change to 'snprintf' for explicit bounds checking | buffer pointer and size may not match"
+          "|string argument is not guaranteed to be null-terminated"
+          "|'va_list' is unsafe}0">;
 def note_unsafe_buffer_operation : Note<
   "used%select{| in pointer arithmetic| in buffer access}0 here">;
 def note_unsafe_buffer_variable_fixit_group : Note<