Fix FP bufferAccessOutOfBounds (#4427)

* Fix FN with buffer size 1

* Fix FP bufferAccessOutOfBounds

Author: chrchr-github

lib/checkbufferoverrun.cpp

@@ -655,7 +655,7 @@ void CheckBufferOverrun::bufferOverflow()
                 if (bufferSize.intvalue <= 0)
                     continue;
                 // buffer size == 1 => do not warn for dynamic memory
-                if (bufferSize.intvalue == 1 && args[argnr]->str() == ".") { // TODO: check if parent was allocated dynamically
+                if (bufferSize.intvalue == 1 && Token::simpleMatch(argtok->astParent(), ".")) { // TODO: check if parent was allocated dynamically
                     const Token *tok2 = argtok;
                     while (Token::simpleMatch(tok2->astParent(), "."))
                         tok2 = tok2->astParent();

test/testbufferoverrun.cpp

@@ -3225,6 +3225,15 @@ class TestBufferOverrun : public TestFixture {
               "    free(p);\n"
               "}\n");
         ASSERT_EQUALS("[test.cpp:4]: (error) Buffer is accessed out of bounds: p\n", errout.str());
+
+        check("typedef struct { char buf[1]; } S;\n"
+              "S* f() {\n"
+              "    S* s = NULL;\n"
+              "    s = (S*)malloc(sizeof(S) + 10);\n"
+              "    sprintf((char*)s->buf, \"abc\");\n"
+              "    return s;\n"
+              "}\n");
+        ASSERT_EQUALS("", errout.str());
     }
 
     void buffer_overrun_errorpath() {