upgrader: Pull using new timestamp-check-from-rev

Both libostree and rpm-ostree support downgrade protection. But what
that means is different between the two. For libostree, downgrade
protection means not fetching any commit which is older than what the
current ref is pointing at. For rpm-ostree, it means not *deploying*
any commit which is older than what the current *deployment* is on.

These two are mostly the same most of the time, but can differ. For
example, on a remote ref which has commits A -> B -> C, where the client
is sitting on a deployment from A, downgrade protection should not
prevent the client from upgrading to B even if there is a newer commit
C.

Since there is no hard relation enforced between what the state of the
OSTree ref is locally and deployments (e.g. we fully support users
manually doing `ostree pull`), it doesn't make sense to compare against
the tip of the ref. Instead, use the new `timestamp-check-from-rev`
to tell libostree to compare against our base revision, which is what we
care about.

Closes: coreos/fedora-coreos-tracker#481

configure.ac

@@ -100,7 +100,7 @@ LIBS="$save_LIBS"
 # Remember to update AM_CPPFLAGS in Makefile.am when bumping GIO req.
 PKG_CHECK_MODULES(PKGDEP_GIO_UNIX, [gio-unix-2.0])
 PKG_CHECK_MODULES(PKGDEP_RPMOSTREE, [gio-unix-2.0 >= 2.50.0 json-glib-1.0
-				     ostree-1 >= 2020.1
+				     ostree-1 >= 2020.4
 				     libsystemd
 				     polkit-gobject-1
 				     rpm librepo libsolv

packaging/rpm-ostree.spec.in

@@ -43,7 +43,7 @@ BuildRequires: gnome-common
 BuildRequires: /usr/bin/g-ir-scanner
 # Core requirements
 # One way to check this: `objdump -p /path/to/rpm-ostree | grep LIBOSTREE` and pick the highest (though that might miss e.g. new struct members)
-BuildRequires: pkgconfig(ostree-1) >= 2019.2
+BuildRequires: pkgconfig(ostree-1) >= 2019.4
 BuildRequires: pkgconfig(polkit-gobject-1)
 BuildRequires: pkgconfig(json-glib-1.0)
 BuildRequires: pkgconfig(rpm)

src/daemon/rpmostree-sysroot-upgrader.c

@@ -416,11 +416,13 @@ rpmostree_sysroot_upgrader_pull_base (RpmOstreeSysrootUpgrader  *self,
                                      g_variant_new_variant (g_variant_new_string (dir_to_pull)));
             g_variant_builder_add (optbuilder, "{s@v}", "flags",
                                    g_variant_new_variant (g_variant_new_int32 (flags)));
-            /* Add the timestamp check, unless disabled. The option was added in
-             * libostree v2017.11 */
+            /* Add the timestamp check, unless disabled or we're fetching a specific commit
+             * since we have no idea where the ostree ref actually is, and that's what
+             * libostree keys off of. Note in the latter case, we still verify that the
+             * fetched commit is newer than the deployment's base revision below. */
             if (!allow_older)
-              g_variant_builder_add (optbuilder, "{s@v}", "timestamp-check",
-                                     g_variant_new_variant (g_variant_new_boolean (TRUE)));
+              g_variant_builder_add (optbuilder, "{s@v}", "timestamp-check-from-rev",
+                                     g_variant_new_variant (g_variant_new_string (self->base_revision)));
             g_variant_builder_add (optbuilder, "{s@v}", "refs",
                                    g_variant_new_variant (g_variant_new_strv (
                                                                               (const char *const *)&origin_ref, 1)));