[clang] [analyzer] New optin.taint.TaintAlloc checker for catching unbounded memory allocation calls (PR #92420)

[Balazs Benics via cfe-commits]

================
@@ -938,6 +938,53 @@ optin.portability.UnixAPI
 """""""""""""""""""""""""
 Finds implementation-defined behavior in UNIX/Posix functions.
 
+.. _optin-taint-TaintAlloc:
+
+optin.taint.TaintAlloc (C, C++)
+"""""""""""""""""""""""""""""""
+
+This checker warns for cases when the ``size`` parameter of the ``malloc`` ,
+``calloc``, ``realloc``, ``alloca`` or the size parameter of the
+array new C++ operator 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 ``alpha.security.taint.TaintPropagation`` checker also needs to be enabled for
+this checker to give warnings.
+
+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 vulnerable(void) {
+    size_t size;
----------------
steakhal wrote:

```suggestion
    size_t size = 0;
```
Let's initialize the value to be similar to the other cases.

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