bpo-34271: Add ssl debugging helpers (GH-10031)

The ssl module now can dump key material to a keylog file and trace TLS
protocol messages with a tracing callback. The default and stdlib
contexts also support SSLKEYLOGFILE env var.

The msg_callback and related enums are private members. The feature
is designed for internal debugging and not for end users.

Signed-off-by: Christian Heimes <christian@python.org>

1 files changed, 213 insertions, 0 deletions

diff --git a/Modules/_ssl/debughelpers.c b/Modules/_ssl/debughelpers.c
new file mode 100644
index 0000000..53b9667
--- /dev/null
+++ b/Modules/_ssl/debughelpers.c
@@ -0,0 +1,213 @@
+/* Debug helpers */
+
+static void
+_PySSL_msg_callback(int write_p, int version, int content_type,
+                    const void *buf, size_t len, SSL *ssl, void *arg)
+{
+    const char *cbuf = (const char *)buf;
+    PyGILState_STATE threadstate;
+    PyObject *res = NULL;
+    PySSLSocket *ssl_obj = NULL;  /* ssl._SSLSocket, borrowed ref */
+    PyObject *ssl_socket = NULL;  /* ssl.SSLSocket or ssl.SSLObject */
+    int msg_type;
+
+    threadstate = PyGILState_Ensure();
+
+    ssl_obj = (PySSLSocket *)SSL_get_app_data(ssl);
+    assert(PySSLSocket_Check(ssl_obj));
+    if (ssl_obj->ctx->msg_cb == NULL) {
+        return;
+    }
+
+    if (ssl_obj->owner)
+        ssl_socket = PyWeakref_GetObject(ssl_obj->owner);
+    else if (ssl_obj->Socket)
+        ssl_socket = PyWeakref_GetObject(ssl_obj->Socket);
+    else
+        ssl_socket = (PyObject *)ssl_obj;
+    Py_INCREF(ssl_socket);
+
+    /* assume that OpenSSL verifies all payload and buf len is of sufficient
+       length */
+    switch(content_type) {
+      case SSL3_RT_CHANGE_CIPHER_SPEC:
+        msg_type = SSL3_MT_CHANGE_CIPHER_SPEC;
+        break;
+      case SSL3_RT_ALERT:
+        /* byte 0: level */
+        /* byte 1: alert type */
+        msg_type = (int)cbuf[1];
+        break;
+      case SSL3_RT_HANDSHAKE:
+        msg_type = (int)cbuf[0];
+        break;
+      case SSL3_RT_HEADER:
+        /* frame header encodes version in bytes 1..2 */
+        version = cbuf[1] << 8 | cbuf[2];
+        msg_type = (int)cbuf[0];
+        break;
+#ifdef SSL3_RT_INNER_CONTENT_TYPE
+      case SSL3_RT_INNER_CONTENT_TYPE:
+        msg_type = (int)cbuf[0];
+        break;
+#endif
+      default:
+        /* never SSL3_RT_APPLICATION_DATA */
+        msg_type = -1;
+        break;
+    }
+
+    res = PyObject_CallFunction(
+        ssl_obj->ctx->msg_cb, "Osiiiy#",
+        ssl_socket, write_p ? "write" : "read",
+        version, content_type, msg_type,
+        buf, len
+    );
+    if (res == NULL) {
+        PyErr_Fetch(&ssl_obj->exc_type, &ssl_obj->exc_value, &ssl_obj->exc_tb);
+    } else {
+        Py_DECREF(res);
+    }
+    Py_XDECREF(ssl_socket);
+
+    PyGILState_Release(threadstate);
+}
+
+
+static PyObject *
+_PySSLContext_get_msg_callback(PySSLContext *self, void *c) {
+    if (self->msg_cb != NULL) {
+        Py_INCREF(self->msg_cb);
+        return self->msg_cb;
+    } else {
+        Py_RETURN_NONE;
+    }
+}
+
+static int
+_PySSLContext_set_msg_callback(PySSLContext *self, PyObject *arg, void *c) {
+    Py_CLEAR(self->msg_cb);
+    if (arg == Py_None) {
+        SSL_CTX_set_msg_callback(self->ctx, NULL);
+    }
+    else {
+        if (!PyCallable_Check(arg)) {
+            SSL_CTX_set_msg_callback(self->ctx, NULL);
+            PyErr_SetString(PyExc_TypeError,
+                            "not a callable object");
+            return -1;
+        }
+        Py_INCREF(arg);
+        self->msg_cb = arg;
+        SSL_CTX_set_msg_callback(self->ctx, _PySSL_msg_callback);
+    }
+    return 0;
+}
+
+#ifdef HAVE_OPENSSL_KEYLOG
+
+static void
+_PySSL_keylog_callback(const SSL *ssl, const char *line)
+{
+    PyGILState_STATE threadstate;
+    PySSLSocket *ssl_obj = NULL;  /* ssl._SSLSocket, borrowed ref */
+    int res, e;
+    static PyThread_type_lock *lock = NULL;
+
+    threadstate = PyGILState_Ensure();
+
+    /* Allocate a static lock to synchronize writes to keylog file.
+     * The lock is neither released on exit nor on fork(). The lock is
+     * also shared between all SSLContexts although contexts may write to
+     * their own files. IMHO that's good enough for a non-performance
+     * critical debug helper.
+     */
+    if (lock == NULL) {
+        lock = PyThread_allocate_lock();
+        if (lock == NULL) {
+            PyErr_SetString(PyExc_MemoryError, "Unable to allocate lock");
+            PyErr_Fetch(&ssl_obj->exc_type, &ssl_obj->exc_value,
+                        &ssl_obj->exc_tb);
+            return;
+        }
+    }
+
+    ssl_obj = (PySSLSocket *)SSL_get_app_data(ssl);
+    assert(PySSLSocket_Check(ssl_obj));
+    if (ssl_obj->ctx->keylog_bio == NULL) {
+        return;
+    }
+
+    PySSL_BEGIN_ALLOW_THREADS
+    PyThread_acquire_lock(lock, 1);
+    res = BIO_printf(ssl_obj->ctx->keylog_bio, "%s\n", line);
+    e = errno;
+    (void)BIO_flush(ssl_obj->ctx->keylog_bio);
+    PyThread_release_lock(lock);
+    PySSL_END_ALLOW_THREADS
+
+    if (res == -1) {
+        errno = e;
+        PyErr_SetFromErrnoWithFilenameObject(PyExc_OSError,
+                                             ssl_obj->ctx->keylog_filename);
+        PyErr_Fetch(&ssl_obj->exc_type, &ssl_obj->exc_value, &ssl_obj->exc_tb);
+    }
+    PyGILState_Release(threadstate);
+}
+
+static PyObject *
+_PySSLContext_get_keylog_filename(PySSLContext *self, void *c) {
+    if (self->keylog_filename != NULL) {
+        Py_INCREF(self->keylog_filename);
+        return self->keylog_filename;
+    } else {
+        Py_RETURN_NONE;
+    }
+}
+
+static int
+_PySSLContext_set_keylog_filename(PySSLContext *self, PyObject *arg, void *c) {
+    FILE *fp;
+    /* Reset variables and callback first */
+    SSL_CTX_set_keylog_callback(self->ctx, NULL);
+    Py_CLEAR(self->keylog_filename);
+    if (self->keylog_bio != NULL) {
+        BIO *bio = self->keylog_bio;
+        self->keylog_bio = NULL;
+        PySSL_BEGIN_ALLOW_THREADS
+        BIO_free_all(bio);
+        PySSL_END_ALLOW_THREADS
+    }
+
+    if (arg == Py_None) {
+        /* None disables the callback */
+        return 0;
+    }
+
+    /* _Py_fopen_obj() also checks that arg is of proper type. */
+    fp = _Py_fopen_obj(arg, "a" PY_STDIOTEXTMODE);
+    if (fp == NULL)
+        return -1;
+
+    self->keylog_bio = BIO_new_fp(fp, BIO_CLOSE | BIO_FP_TEXT);
+    if (self->keylog_bio == NULL) {
+        PyErr_SetString(PySSLErrorObject,
+                        "Can't malloc memory for keylog file");
+        return -1;
+    }
+    Py_INCREF(arg);
+    self->keylog_filename = arg;
+
+    /* Write a header for seekable, empty files (this excludes pipes). */
+    PySSL_BEGIN_ALLOW_THREADS
+    if (BIO_tell(self->keylog_bio) == 0) {
+        BIO_puts(self->keylog_bio,
+                 "# TLS secrets log file, generated by OpenSSL / Python\n");
+        (void)BIO_flush(self->keylog_bio);
+    }
+    PySSL_END_ALLOW_THREADS
+    SSL_CTX_set_keylog_callback(self->ctx, _PySSL_keylog_callback);
+    return 0;
+}
+
+#endif
\ No newline at end of file