[Libguestfs] bug in gnutls_init()

I just fixed a bug in nbdkit for incorrectly calling free(gnutls_session_t) after gnutls_init(&session, ...) fails: https://gitlab.com/nbdkit/nbdkit/-/commit/40faf3dfb20c06b9c5faa0a122607e3... But in the process, I was browsing the source code to gnutls_init() to see why Coverity wasn't flagging free(opaque_type) as fishy, and found that there is a nasty lurking bug: int gnutls_init(gnutls_session_t * session, unsigned int flags) { int ret; FAIL_IF_LIB_ERROR; *session = gnutls_calloc(1, sizeof(struct gnutls_session_int)); Note that *session is left uninitialized if FAIL_IF_LIB_ERROR; causes an early return GNUTLS_E_LIB_IN_ERROR_STATE. If a caller (properly) treats gnutls_session_t as an opaque type, and does not try to zero-initialize it (as there is no way to know that 0 is a safe value for an opaque type), then writing: gnutls_session_t session; int err = gnutls_init (&session, GNUTLS_SERVER); if (err < 0) gnutls_deinit (session); is a bug waiting to happen, because it WILL cause gnutls_deinit() to attempt to dereference an uninitialized pointer if session remains uninitialized because of an earlier library error. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org