Don't accept ranges for add commands in consdiff

Fixes ticket #21963

src/or/consdiff.c

@@ -795,6 +795,7 @@ apply_ed_diff(const smartlist_t *cons1, const smartlist_t *diff,
     diff_line[diff_cdline->len] = 0;
     const char *ptr = diff_line;
     int start = 0, end = 0;
+    int had_range = 0;
     if (get_linenum(&ptr, &start) < 0) {
       log_warn(LD_CONSDIFF, "Could not apply consensus diff because "
                "an ed command was missing a line number.");
@@ -802,6 +803,7 @@ apply_ed_diff(const smartlist_t *cons1, const smartlist_t *diff,
     }
     if (*ptr == ',') {
       /* Two-item range */
+      had_range = 1;
       ++ptr;
       if (get_linenum(&ptr, &end) < 0) {
         log_warn(LD_CONSDIFF, "Could not apply consensus diff because "
@@ -850,6 +852,13 @@ apply_ed_diff(const smartlist_t *cons1, const smartlist_t *diff,
         goto error_cleanup;
     }
 
+    /* 'a' commands are not allowed to have ranges. */
+    if (had_range && action == 'a') {
+      log_warn(LD_CONSDIFF, "Could not apply consensus diff because "
+          "it wanted to add lines after a range.");
+      goto error_cleanup;
+    }
+
     /* Add unchanged lines. */
     for (; j && j > end; --j) {
       cdline_t *cons_line = smartlist_get(cons1, j-1);

src/test/test_consdiff.c

@@ -687,6 +687,15 @@ test_consdiff_apply_ed_diff(void *arg)
 
   smartlist_clear(diff);
 
+  /* Unexpected range for add command. */
+  smartlist_add_linecpy(diff, area, "1,2a");
+  mock_clean_saved_logs();
+  cons2 = apply_ed_diff(cons1, diff, 0);
+  tt_ptr_op(NULL, OP_EQ, cons2);
+  expect_single_log_msg_containing("add lines after a range");
+
+  smartlist_clear(diff);
+
   /* Script is not in reverse order. */
   smartlist_add_linecpy(diff, area, "1d");
   smartlist_add_linecpy(diff, area, "3d");