fix potential race condition in ALTS integrity-only extra-copy mode

src/core/tsi/alts/zero_copy_frame_protector/alts_grpc_integrity_only_record_protocol.cc

@@ -42,34 +42,34 @@ typedef struct alts_grpc_integrity_only_record_protocol {
 static tsi_result alts_grpc_integrity_only_extra_copy_protect(
     alts_grpc_record_protocol* rp, grpc_slice_buffer* unprotected_slices,
     grpc_slice_buffer* protected_slices) {
-  /* Allocates memory for protected frame.  */
+  /* Allocates memory for protected frame and copies data.  */
+  size_t data_length = unprotected_slices->length;
   size_t protected_frame_size =
       unprotected_slices->length + rp->header_length + rp->tag_length;
   grpc_slice protected_slice = GRPC_SLICE_MALLOC(protected_frame_size);
+  uint8_t* data = GRPC_SLICE_START_PTR(protected_slice) + rp->header_length;
+  for (size_t i = 0; i < unprotected_slices->count; i++) {
+    memcpy(data, GRPC_SLICE_START_PTR(unprotected_slices->slices[i]),
+           GRPC_SLICE_LENGTH(unprotected_slices->slices[i]));
+    data += GRPC_SLICE_LENGTH(unprotected_slices->slices[i]);
+  }
   /* Calls alts_iovec_record_protocol protect.  */
   char* error_details = nullptr;
   iovec_t header_iovec = {GRPC_SLICE_START_PTR(protected_slice),
                           rp->header_length};
-  iovec_t tag_iovec = {GRPC_SLICE_START_PTR(protected_slice) +
-                           rp->header_length + unprotected_slices->length,
-                       rp->tag_length};
-  alts_grpc_record_protocol_convert_slice_buffer_to_iovec(rp,
-                                                          unprotected_slices);
+  iovec_t tag_iovec = {
+      GRPC_SLICE_START_PTR(protected_slice) + rp->header_length + data_length,
+      rp->tag_length};
+  rp->iovec_buf[0].iov_base =
+      GRPC_SLICE_START_PTR(protected_slice) + rp->header_length;
+  rp->iovec_buf[0].iov_len = data_length;
   grpc_status_code status = alts_iovec_record_protocol_integrity_only_protect(
-      rp->iovec_rp, rp->iovec_buf, unprotected_slices->count, header_iovec,
-      tag_iovec, &error_details);
+      rp->iovec_rp, rp->iovec_buf, 1, header_iovec, tag_iovec, &error_details);
   if (status != GRPC_STATUS_OK) {
     gpr_log(GPR_ERROR, "Failed to protect, %s", error_details);
     gpr_free(error_details);
     return TSI_INTERNAL_ERROR;
   }
-  /* Copies data from unprotected_slices to protected_slice.  */
-  uint8_t* data = GRPC_SLICE_START_PTR(protected_slice) + rp->header_length;
-  for (size_t i = 0; i < unprotected_slices->count; i++) {
-    memcpy(data, GRPC_SLICE_START_PTR(unprotected_slices->slices[i]),
-           GRPC_SLICE_LENGTH(unprotected_slices->slices[i]));
-    data += GRPC_SLICE_LENGTH(unprotected_slices->slices[i]);
-  }
   grpc_slice_buffer_add(protected_slices, protected_slice);
   grpc_slice_buffer_reset_and_unref_internal(unprotected_slices);
   return TSI_OK;