verify: enforce format transitions

When using verify's -m option, it generally only makes sense to verify a
build within the same format, since the subsequent format (if any) might
not be compatible. Therefore, we should disallow verifying to a build
with a different format by default. This commit adds the proper
enforcement by making this condition a fatal error. The early exit can
be bypassed using the -x/--force option, which will print a warning
message instead.

For now, this compatibility check is targeting the use case of verifying
to a newer build, so I also report the latest supported build for the
current format. Verifying to an older build is not guaranteed to succeed
at present, and swupd-client does not yet understand the
version/formatN/first file. In other words, reporting to the user the
oldest build they can verify to will be a future improvement.

Signed-off-by: Patrick McCarty <patrick.mccarty@intel.com>

include/swupd.h

@@ -331,6 +331,7 @@ extern struct list *files_from_bundles(struct list *bundles);
 extern bool version_files_consistent(void);
 extern bool string_in_list(char *string_to_check, struct list *list_to_check);
 extern void print_progress(unsigned int count, unsigned int max);
+extern bool is_compatible_format(int format_num);
 
 /* subscription.c */
 struct list *free_list_file(struct list *item);

src/helpers.c

@@ -965,3 +965,28 @@ void print_progress(unsigned int count, unsigned int max)
 		}
 	}
 }
+
+/* Compare formats of the global variable (format_string) and the format number
+ * from a manifest (usually a MoM). Because "staging" is treated specially and
+ * never appears in a manifest, it is skipped. */
+bool is_compatible_format(int format_num)
+{
+	if (strcmp(format_string, "staging") == 0) {
+		return true;
+	}
+
+	char *format_manifest = NULL;
+	string_or_die(&format_manifest, "%d", format_num);
+
+	size_t len = strlen(format_string);
+
+	bool ret;
+	if (strncmp(format_string, format_manifest, len) == 0) {
+		ret = true;
+	} else {
+		ret = false;
+	}
+
+	free(format_manifest);
+	return ret;
+}

src/verify.c

@@ -702,6 +702,23 @@ int verify_main(int argc, char **argv)
 		goto clean_and_exit;
 	}
 
+	if (!is_compatible_format(official_manifest->manifest_version)) {
+		if (force) {
+			fprintf(stderr, "WARNING: the force option is specified; ignoring"
+					" format mismatch for verify\n");
+		} else {
+			fprintf(stderr, "ERROR: Mismatching formats detected when verifying %d"
+					" (expected: %s; actual: %d)\n",
+				version, format_string, official_manifest->manifest_version);
+			int latest = get_latest_version();
+			if (latest > 0) {
+				fprintf(stderr, "Latest supported version to verify: %d\n", latest);
+			}
+			ret = EMANIFEST_LOAD;
+			goto clean_and_exit;
+		}
+	}
+
 	ret = add_included_manifests(official_manifest, version, &subs);
 	if (ret) {
 		ret = EMANIFEST_LOAD;