Improper Null Termination

Summary

Golioth Firmware SDK version 0.19.1 prior to 0.22.0, fixed in commit 0e788217, contain an out-of-bounds read due to improper null termination of a blockwise transfer path. blockwise_transfer_init() accepts a path whose length equals CONFIG_GOLIOTH_COAP_MAX_PATH_LEN and copies it using strncpy() without guaranteeing a trailing NUL byte, leaving ctx->path unterminated. A later strlen() on this buffer (in golioth_coap_client_get_internal()) can read past the end of the allocation, resulting in a crash/denial of service. The input is application-controlled (not network by default).