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/40faf3dfb20c06b9c5faa0a122607e3ae7c6202a
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
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