CVE-2021-37686: Infinite loop in TFLite

The strided slice implementation in TFLite has a logic bug which can allow an attacker to trigger an infinite loop. This arises from newly introduced support for ellipsis in axis definition:

for (int i = 0; i < effective_dims;) {
if ((1 << i) & op_context->params->ellipsis_mask) {
// ...
int ellipsis_end_idx =
std::min(i + 1 + num_add_axis + op_context->input_dims - begin_count,
effective_dims);
// ...
for (; i < ellipsis_end_idx; ++i) {
// ...
}
continue;
}
// ...
++i;
}

An attacker can craft a model such that ellipsis_end_idx is smaller than i (e.g., always negative). In this case, the inner loop does not increase i and the continue statement causes execution to skip over the preincrement at the end of the outer loop.