extmod/modtls_mbedtls: Add a thread-global ptr for current SSL context.

This is necessary for mbedTLS callbacks that do not carry any user state,
so those callbacks can be customised per SSL context.

Signed-off-by: iabdalkader <i.abdalkader@gmail.com>

Author: iabdalkader

extmod/modtls_mbedtls.c

@@ -166,6 +166,13 @@ static NORETURN void mbedtls_raise_error(int err) {
     #endif
 }
 
+// Stores the current SSLContext for use in mbedtls callbacks where the current state is not passed.
+static inline void store_active_context(mp_obj_ssl_context_t *ssl_context) {
+    #if MICROPY_PY_SSL_MBEDTLS_NEED_ACTIVE_CONTEXT
+    MP_STATE_THREAD(tls_ssl_context) = ssl_context;
+    #endif
+}
+
 static void ssl_check_async_handshake_failure(mp_obj_ssl_socket_t *sslsock, int *errcode) {
     if (
         #if MBEDTLS_VERSION_NUMBER >= 0x03000000
@@ -497,6 +504,9 @@ static int _mbedtls_ssl_recv(void *ctx, byte *buf, size_t len) {
 static mp_obj_t ssl_socket_make_new(mp_obj_ssl_context_t *ssl_context, mp_obj_t sock,
     bool server_side, bool do_handshake_on_connect, mp_obj_t server_hostname) {
 
+    // Store the current SSL context.
+    store_active_context(ssl_context);
+
     // Verify the socket object has the full stream protocol
     mp_get_stream_raise(sock, MP_STREAM_OP_READ | MP_STREAM_OP_WRITE | MP_STREAM_OP_IOCTL);
 
@@ -602,6 +612,9 @@ static mp_uint_t socket_read(mp_obj_t o_in, void *buf, mp_uint_t size, int *errc
         return MP_STREAM_ERROR;
     }
 
+    // Store the current SSL context.
+    store_active_context(o->ssl_context);
+
     int ret = mbedtls_ssl_read(&o->ssl, buf, size);
     if (ret == MBEDTLS_ERR_SSL_PEER_CLOSE_NOTIFY) {
         // end of stream
@@ -643,6 +656,9 @@ static mp_uint_t socket_write(mp_obj_t o_in, const void *buf, mp_uint_t size, in
         return MP_STREAM_ERROR;
     }
 
+    // Store the current SSL context.
+    store_active_context(o->ssl_context);
+
     int ret = mbedtls_ssl_write(&o->ssl, buf, size);
     if (ret >= 0) {
         return ret;
@@ -680,6 +696,9 @@ static mp_uint_t socket_ioctl(mp_obj_t o_in, mp_uint_t request, uintptr_t arg, i
     mp_obj_t sock = self->sock;
 
     if (request == MP_STREAM_CLOSE) {
+        // Clear the SSL context.
+        store_active_context(NULL);
+
         if (sock == MP_OBJ_NULL) {
             // Already closed socket, do nothing.
             return 0;

py/mpconfig.h

@@ -1814,6 +1814,11 @@ typedef double mp_float_t;
 #define MICROPY_PY_SSL_FINALISER (MICROPY_ENABLE_FINALISER)
 #endif
 
+// Whether to add a root pointer for the current ssl object
+#ifndef MICROPY_PY_SSL_MBEDTLS_NEED_ACTIVE_CONTEXT
+#define MICROPY_PY_SSL_MBEDTLS_NEED_ACTIVE_CONTEXT (MICROPY_PY_SSL_ECDSA_SIGN_ALT)
+#endif
+
 // Whether to provide the "vfs" module
 #ifndef MICROPY_PY_VFS
 #define MICROPY_PY_VFS (MICROPY_CONFIG_ROM_LEVEL_AT_LEAST_CORE_FEATURES && MICROPY_VFS)

py/mpstate.h

@@ -293,6 +293,10 @@ typedef struct _mp_state_thread_t {
     bool prof_callback_is_executing;
     struct _mp_code_state_t *current_code_state;
     #endif
+
+    #if MICROPY_PY_SSL_MBEDTLS_NEED_ACTIVE_CONTEXT
+    struct _mp_obj_ssl_context_t *tls_ssl_context;
+    #endif
 } mp_state_thread_t;
 
 // This structure combines the above 3 structures.