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Our recent code security fixes made malloc check

  tor_assert(size < SIZE_T_CEILING);

but we didn't add a similar check to tor_realloc().

Assuming we do add it, doors pointed out another gotcha:

In tor_gzip_uncompress() we

        *out = tor_realloc(*out, out_size);
        stream->next_out = (unsigned char*)(*out + offset);
        if (out_size - offset > UINT_MAX) {
          log_warn(LD_BUG,  "Ran over unsigned int limit of zlib while "
                   "uncompressing.");
          goto err;
        }

And since the largest compressed blob we'll accept is MAX_DIR_DL_SIZE (16MBish), a compress bomb (e.g. a consensus answer) could create a string that's more than SIZE_T_CEILING yet less than UINT_MAX, thus remotely triggering the assert in tor_realloc.