[clang][analyzer] Add function 'fscanf' to StreamChecker. (#78180)

Author: balazske

clang/lib/StaticAnalyzer/Checkers/StreamChecker.cpp

@@ -266,6 +266,9 @@ class StreamChecker : public Checker<check::PreCall, eval::Call,
       {{{"fprintf"}},
        {std::bind(&StreamChecker::preReadWrite, _1, _2, _3, _4, false),
         std::bind(&StreamChecker::evalFprintf, _1, _2, _3, _4), 0}},
+      {{{"fscanf"}},
+       {std::bind(&StreamChecker::preReadWrite, _1, _2, _3, _4, true),
+        std::bind(&StreamChecker::evalFscanf, _1, _2, _3, _4), 0}},
       {{{"ungetc"}, 2},
        {std::bind(&StreamChecker::preReadWrite, _1, _2, _3, _4, false),
         std::bind(&StreamChecker::evalUngetc, _1, _2, _3, _4), 1}},
@@ -345,6 +348,9 @@ class StreamChecker : public Checker<check::PreCall, eval::Call,
   void evalFprintf(const FnDescription *Desc, const CallEvent &Call,
                    CheckerContext &C) const;
 
+  void evalFscanf(const FnDescription *Desc, const CallEvent &Call,
+                  CheckerContext &C) const;
+
   void evalUngetc(const FnDescription *Desc, const CallEvent &Call,
                   CheckerContext &C) const;
 
@@ -975,6 +981,69 @@ void StreamChecker::evalFprintf(const FnDescription *Desc,
   C.addTransition(StateFailed);
 }
 
+void StreamChecker::evalFscanf(const FnDescription *Desc, const CallEvent &Call,
+                               CheckerContext &C) const {
+  ProgramStateRef State = C.getState();
+  if (Call.getNumArgs() < 2)
+    return;
+  SymbolRef StreamSym = getStreamArg(Desc, Call).getAsSymbol();
+  if (!StreamSym)
+    return;
+
+  const CallExpr *CE = dyn_cast_or_null<CallExpr>(Call.getOriginExpr());
+  if (!CE)
+    return;
+
+  const StreamState *OldSS = State->get<StreamMap>(StreamSym);
+  if (!OldSS)
+    return;
+
+  assertStreamStateOpened(OldSS);
+
+  SValBuilder &SVB = C.getSValBuilder();
+  ASTContext &ACtx = C.getASTContext();
+
+  // Add the success state.
+  // In this context "success" means there is not an EOF or other read error
+  // before any item is matched in 'fscanf'. But there may be match failure,
+  // therefore return value can be 0 or greater.
+  // It is not specified what happens if some items (not all) are matched and
+  // then EOF or read error happens. Now this case is handled like a "success"
+  // case, and no error flags are set on the stream. This is probably not
+  // accurate, and the POSIX documentation does not tell more.
+  if (OldSS->ErrorState != ErrorFEof) {
+    NonLoc RetVal = makeRetVal(C, CE).castAs<NonLoc>();
+    ProgramStateRef StateNotFailed =
+        State->BindExpr(CE, C.getLocationContext(), RetVal);
+    auto RetGeZero =
+        SVB.evalBinOp(StateNotFailed, BO_GE, RetVal,
+                      SVB.makeZeroVal(ACtx.IntTy), SVB.getConditionType())
+            .getAs<DefinedOrUnknownSVal>();
+    if (!RetGeZero)
+      return;
+    StateNotFailed = StateNotFailed->assume(*RetGeZero, true);
+
+    C.addTransition(StateNotFailed);
+  }
+
+  // Add transition for the failed state.
+  // Error occurs if nothing is matched yet and reading the input fails.
+  // Error can be EOF, or other error. At "other error" FERROR or 'errno' can
+  // be set but it is not further specified if all are required to be set.
+  // Documentation does not mention, but file position will be set to
+  // indeterminate similarly as at 'fread'.
+  ProgramStateRef StateFailed = bindInt(*EofVal, State, C, CE);
+  StreamErrorState NewES = (OldSS->ErrorState == ErrorFEof)
+                               ? ErrorFEof
+                               : ErrorNone | ErrorFEof | ErrorFError;
+  StreamState NewSS = StreamState::getOpened(Desc, NewES, !NewES.isFEof());
+  StateFailed = StateFailed->set<StreamMap>(StreamSym, NewSS);
+  if (OldSS->ErrorState != ErrorFEof)
+    C.addTransition(StateFailed, constructSetEofNoteTag(C, StreamSym));
+  else
+    C.addTransition(StateFailed);
+}
+
 void StreamChecker::evalUngetc(const FnDescription *Desc, const CallEvent &Call,
                                CheckerContext &C) const {
   ProgramStateRef State = C.getState();

clang/test/Analysis/stream-error.c

@@ -208,6 +208,31 @@ void error_fprintf(void) {
   fprintf(F, "ccc"); // expected-warning {{Stream might be already closed}}
 }
 
+void error_fscanf(int *A) {
+  FILE *F = tmpfile();
+  if (!F)
+    return;
+  int Ret = fscanf(F, "a%ib", A);
+  if (Ret >= 0) {
+    clang_analyzer_eval(feof(F) || ferror(F)); // expected-warning {{FALSE}}
+    fscanf(F, "bbb");                          // no-warning
+  } else {
+    if (ferror(F)) {
+      clang_analyzer_warnIfReached(); // expected-warning {{REACHABLE}}
+      fscanf(F, "bbb");               // expected-warning {{might be 'indeterminate'}}
+    } else if (feof(F)) {
+      clang_analyzer_warnIfReached(); // expected-warning {{REACHABLE}}
+      fscanf(F, "bbb");               // expected-warning {{is in EOF state}}
+      clang_analyzer_eval(feof(F));   // expected-warning {{TRUE}}
+    } else {
+      clang_analyzer_warnIfReached(); // expected-warning {{REACHABLE}}
+      fscanf(F, "bbb");               // expected-warning {{might be 'indeterminate'}}
+    }
+  }
+  fclose(F);
+  fscanf(F, "ccc"); // expected-warning {{Stream might be already closed}}
+}
+
 void error_ungetc() {
   FILE *F = tmpfile();
   if (!F)

clang/test/Analysis/stream.c

@@ -45,6 +45,12 @@ void check_fprintf(void) {
   fclose(fp);
 }
 
+void check_fscanf(void) {
+  FILE *fp = tmpfile();
+  fscanf(fp, "ABC"); // expected-warning {{Stream pointer might be NULL}}
+  fclose(fp);
+}
+
 void check_ungetc(void) {
   FILE *fp = tmpfile();
   ungetc('A', fp); // expected-warning {{Stream pointer might be NULL}}