[clang] [analyzer] Adding taint analysis capability to unix.Malloc checker (PR #92420)

[Balazs Benics via cfe-commits]

================
@@ -1273,6 +1273,41 @@ Check for memory leaks, double free, and use-after-free problems. Traces memory
 .. literalinclude:: checkers/unix_malloc_example.c
     :language: c
 
+If the ``alpha.security.taint.TaintPropagation`` checker is enabled, the checker
+warns for cases when the ``size`` parameter of the ``malloc`` , ``calloc``,
+``realloc``, ``alloca`` is tainted (potentially attacker controlled). If an
+attacker can inject a large value as the size parameter, memory exhaustion
+denial of service attack can be carried out.
+
+The analyzer emits warning only if it cannot prove that the size parameter is
+within reasonable bounds (``<= SIZE_MAX/4``). This functionality partially
+covers the SEI Cert coding standard rule `INT04-C
+<https://wiki.sei.cmu.edu/confluence/display/c/INT04-C.+Enforce+limits+on+integer+values+originating+from+tainted+sources>`_.
+
+You can silence this warning either by bound checking the ``size`` parameter, or
+by explicitly marking the ``size`` parameter as sanitized. See the
+:ref:`alpha-security-taint-TaintPropagation` checker for more details.
+
+.. code-block:: c
+
+  void t1(void) {
+    size_t size;
+    scanf("%zu", &size);
+    int *p = malloc(size); // warn: malloc is called with a tainted (potentially attacker controlled) value
+    free(p);
+  }
+
+  void t3(void) {
+    size_t size;
+    scanf("%zu", &size);
+    if (1024<size)
----------------
steakhal wrote:

```suggestion
    size_t size = 0;
    scanf("%zu", &size);
    if (1024 < size)
```
Format code; initialize `size` to have a defined value even if `scanf` fails.

https://github.com/llvm/llvm-project/pull/92420