warn when buffer is not zero terminated after strncpy

lib/checkbufferoverrun.cpp

@@ -155,15 +155,22 @@ void CheckBufferOverrun::sizeArgumentAsCharError(const Token *tok)
 }
 
 
-void CheckBufferOverrun::terminateStrncpyError(const Token *tok, const std::string &varname)
+void CheckBufferOverrun::terminateStrncpyError(const Token *tok, const std::string &varname, bool conclusive)
 {
-    reportError(tok, Severity::warning, "terminateStrncpy",
+    if (conclusive)
-                "The buffer '" + varname + "' may not be zero-terminated after the call to strncpy().\n"
+        reportError(tok, Severity::warning, "terminateStrncpy",
-                "The use of strncpy() usually indicates that the programmer wants to ensure "
+                    "The buffer '" + varname + "' is not zero-terminated after the call to strncpy().\n"
-                "the buffer is zero-terminated after the call. However if the (buffer) size given for "
+                    "The use of strncpy() usually indicates that the programmer wants to ensure "
-                "the strncpy() call matches the actual buffer size strncpy() does not add the "
+                    "the buffer is zero-terminated after the call. This will cause bugs later in the code if "
-                "zero at the end of the buffer. This may cause bugs later in the code if "
+                    "the code assumes buffer is zero-terminated.");
-                "the code assumes buffer is zero-terminated.");
+    else
+        reportError(tok, Severity::warning, "terminateStrncpy",
+                    "The buffer '" + varname + "' may not be zero-terminated after the call to strncpy().\n"
+                    "The use of strncpy() usually indicates that the programmer wants to ensure "
+                    "the buffer is zero-terminated after the call. However if the (buffer) size given for "
+                    "the strncpy() call matches the actual buffer size strncpy() does not add the "
+                    "zero at the end of the buffer. This may cause bugs later in the code if "
+                    "the code assumes buffer is zero-terminated.");
 }
 
 void CheckBufferOverrun::cmdLineArgsError(const Token *tok)
@@ -1221,6 +1228,16 @@ void CheckBufferOverrun::checkScope(const Token *tok, const ArrayInfo &arrayInfo
             checkFunctionCall(tok, arrayInfo);
         }
 
+        if (Token::Match(tok, "strncpy ( %varid% , %str% , %num% )", arrayInfo.varid()))
+        {
+            unsigned int num = (unsigned int)MathLib::toLongNumber(tok->strAt(6));
+            if (Token::getStrLength(tok->tokAt(4)) >= total_size && total_size == num)
+            {
+                if (_settings->inconclusive)
+                    terminateStrncpyError(tok, tok->strAt(2), true);
+            }
+        }
+
         if ((Token::Match(tok, "strncpy|strncat ( %varid% , %var% , %num% )", arrayInfo.varid())) ||
             (Token::Match(tok, "strncpy|strncat ( %varid% , %var% [ %any% ] , %num% )", arrayInfo.varid())))
         {
@@ -1243,7 +1260,7 @@ void CheckBufferOverrun::checkScope(const Token *tok, const ArrayInfo &arrayInfo
                             {
                                 // this is currently 'inconclusive'. See TestBufferOverrun::terminateStrncpy3
                                 if (_settings->isEnabled("style") && _settings->inconclusive)
-                                    terminateStrncpyError(tok, tok->strAt(2));
+                                    terminateStrncpyError(tok, tok->strAt(2), false);
                             }
 
                             break;

lib/checkbufferoverrun.h

@@ -216,7 +216,7 @@ public:
     void strncatUsageError(const Token *tok);
     void outOfBoundsError(const Token *tok, const std::string &what);
     void sizeArgumentAsCharError(const Token *tok);
-    void terminateStrncpyError(const Token *tok, const std::string &varname);
+    void terminateStrncpyError(const Token *tok, const std::string &varname, bool conclusive);
     void negativeIndexError(const Token *tok, MathLib::bigint index);
     void cmdLineArgsError(const Token *tok);
     void pointerOutOfBoundsError(const Token *tok, const std::string &object);	// UB when result of calculation is out of bounds
@@ -231,7 +231,7 @@ public:
         c.strncatUsageError(0);
         c.outOfBoundsError(0, "index");
         c.sizeArgumentAsCharError(0);
-        c.terminateStrncpyError(0, "buffer");
+        c.terminateStrncpyError(0, "buffer", false);
         c.negativeIndexError(0, -1);
         c.cmdLineArgsError(0);
         c.pointerOutOfBoundsError(0, "array");

test/testbufferoverrun.cpp

@@ -2908,7 +2908,7 @@ private:
               " char c[6];\n"
               " strncpy(c,\"hello!\",sizeof(c));\n"
               "}\n");
-        ASSERT_EQUALS("", errout.str());
+        ASSERT_EQUALS("[test.cpp:4]: (warning) The buffer 'c' is not zero-terminated after the call to strncpy().\n", errout.str());
 
         check("void f()\n"
               "{\n"