Merge pull request Mbed-TLS#9065 from paul-elliott-arm/fix_ubsan_mp_aead_gcm

Add early exit if zero length AEAD additional data passed in.

Author: gilles-peskine-arm

ChangeLog.d/fix_ubsan_mp_aead_gcm.txt

@@ -0,0 +1,3 @@
+Bugfix
+   * Fix undefined behaviour (incrementing a NULL pointer by zero length) when
+     passing in zero length additional data to multipart AEAD.

library/psa_crypto.c

@@ -5194,6 +5194,12 @@ psa_status_t psa_aead_update_ad(psa_aead_operation_t *operation,
         goto exit;
     }
 
+    /* No input to add (zero length), nothing to do. */
+    if (input_length == 0) {
+        status = PSA_SUCCESS;
+        goto exit;
+    }
+
     if (operation->lengths_set) {
         if (operation->ad_remaining < input_length) {
             status = PSA_ERROR_INVALID_ARGUMENT;