For RHEL we want apps to use FIPS-certified crypto libraries,
and HMAC apparently counts as "keyed" and hence needs to
be validated.
Bug: https://bugzilla.redhat.com/show_bug.cgi?id=1630260
Replaces: https://gitlab.gnome.org/GNOME/glib/merge_requests/897
This is a build-time option that backs the GHmac API with GnuTLS.
Most distributors ship glib-networking built with GnuTLS, and
most apps use glib-networking, so this isn't a net-new library
in most cases.
=======================================================================
mcatanzaro note:
I've updated Colin's original patch with several enhancements:
Implement g_hmac_copy() using gnutls_hmac_copy(), which didn't exist
when Colin developed this patch.
Removed use of GSlice
Better error checking in g_hmac_new(). It is possible for
gnutls_hmac_init() to fail if running in FIPS mode and an MD5 digest is
requested. In this case, we should return NULL rather than returning a
broken GHmac with a NULL gnutls_hmac_hd_t. This was leading to a later
null pointer dereference inside gnutls_hmac_update(). Applications are
responsible for checking to ensure the return value of g_hmac_new() is
not NULL since it is annotated as nullable. Added documentation to
indicate this possibility.
Properly handle length -1 in g_hmac_update(). This means we've been
given a NUL-terminated string and should use strlen(). GnuTLS doesn't
accept -1, so let's call strlen() ourselves.
Crash the application with g_error() if gnutls_hmac() fails for any
reason. This is necessary because g_hmac_update() is not fallible, so we
have no way to indicate error. Crashing seems better than returning the
wrong result later when g_hmac_get_string() or g_hmac_get_digest() is
later called. (Those functions are also not fallible.) Fortunately, I
don't think this error should actually be hit in practice.
https://gitlab.gnome.org/GNOME/glib/-/merge_requests/903
