[PATCH v2025.09.y 57/58] FIT: reconstruct hashed-nodes property during verification

[Ahmad Fatoum]

From: Sascha Hauer <s.hauer at pengutronix.de>

The hashed-nodes property in FIT signed image configurations is used to
determine which nodes are hashed, but is itself not hashed, so could be
manipulated.

To fix this do not use the hashed-nodes property to calculate which
nodes must be hashed, but instead reconstruct the hashed nodes list by
the images used in a FIT configuration, the same way mkimage does it
when creating the image.

The approach mirrors U-Boot commit 2092322b31c ("boot: Add
fit_config_get_hash_list() to build signed node list")

Fixes: ac55adb321 ("bootm: add initial FIT support")
Signed-off-by: Sascha Hauer <s.hauer at pengutronix.de>
Reviewed-by: Ahmad Fatoum <a.fatoum at pengutronix.de>
Tested-by: Ahmad Fatoum <a.fatoum at pengutronix.de>
Link: https://lore.kernel.org/barebox/859a45ba-28c0-4d37-853f-39529ab2521b@pengutronix.de
---
 common/image-fit.c | 123 ++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 106 insertions(+), 17 deletions(-)

diff --git a/common/image-fit.c b/common/image-fit.c
index 9748e5f1d8f0..eae6e6efcf64 100644
--- a/common/image-fit.c
+++ b/common/image-fit.c
@@ -55,18 +55,6 @@ static char *dt_string(struct fdt_header *f, char *strstart, uint32_t ofs)
 		return strstart + ofs;
 }
 
-static int of_read_string_list(struct device_node *np, const char *name, struct string_list *sl)
-{
-	struct property *prop;
-	const char *s;
-
-	of_property_for_each_string(np, name, prop, s) {
-		string_list_add(sl, s);
-	}
-
-	return prop ? 0 : -EINVAL;
-}
-
 static int fit_digest(struct fit_handle *handle, struct digest *digest,
 		      struct string_list *inc_nodes, struct string_list *exc_props,
 		      uint32_t hashed_strings_start, uint32_t hashed_strings_size)
@@ -312,10 +300,106 @@ static int fit_check_signature(struct fit_handle *handle, struct device_node *si
 	return 0;
 }
 
+static int fit_config_build_hash_nodes(struct fit_handle *handle,
+				       struct device_node *conf_node,
+				       struct string_list *node_list)
+{
+	struct device_node *image_node, *child;
+	struct property *prop;
+	const char *unit;
+	int i, ret, count;
+
+	ret = string_list_add(node_list, "/");
+	if (ret)
+		return ret;
+	ret = string_list_add_asprintf(node_list, "%s", conf_node->full_name);
+	if (ret)
+		return ret;
+
+	for_each_property_of_node(conf_node, prop) {
+		if (!strcmp(prop->name, "description") ||
+		    !strcmp(prop->name, "compatible") ||
+		    !strcmp(prop->name, "default"))
+			continue;
+
+		count = of_property_count_strings(conf_node, prop->name);
+		for (i = 0; i < count; i++) {
+			if (of_property_read_string_index(conf_node, prop->name,
+							  i, &unit))
+				return -EINVAL;
+
+			if (strchr(unit, '/'))
+				return -EINVAL;
+
+			ret = string_list_add_asprintf(node_list, "/images/%s", unit);
+			if (ret)
+				return ret;
+
+			image_node = of_get_child_by_name(handle->images, unit);
+			if (!image_node)
+				return -EINVAL;
+
+			for_each_child_of_node(image_node, child) {
+				if (!of_node_has_prefix(child, "hash"))
+					continue;
+				ret = string_list_add_asprintf(node_list, "/images/%s/%s",
+							       unit, child->name);
+				if (ret)
+					return ret;
+			}
+		}
+	}
+
+	return 0;
+}
+
+static int fit_config_check_hash_nodes(struct device_node *sig_node,
+				       struct string_list *inc_nodes)
+{
+	struct string_list *entry;
+	const char *node;
+	int ret, i = 0;
+
+	/*
+	 * Check if the hashed-nodes property matches the list of nodes we calculated.
+	 * We don't use the hashed-nodes property finally, but let's check for consistency
+	 * to inform the user if something is wrong.
+	 */
+
+	string_list_for_each_entry(entry, inc_nodes) {
+
+		ret = of_property_read_string_index(sig_node, "hashed-nodes", i, &node);
+		if (ret) {
+			pr_err("Cannot read hashed-node[%u]: %pe\n", i,
+			       ERR_PTR(ret));
+			return ret;
+		}
+
+		if (strcmp(entry->str, node)) {
+			pr_err("hashed-node[%u] doesn't match calculated node: %s != %s\n",
+			       i, entry->str, node);
+			return -EINVAL;
+		}
+
+		i++;
+	}
+
+	ret = of_property_read_string_index(sig_node, "hashed-nodes", i,
+					    &node);
+	if (!ret) {
+		pr_err("hashed-nodes property has more entries than we calculated\n");
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
 /*
  * The consistency of the FTD structure was already checked by of_unflatten_dtb()
  */
-static int fit_verify_signature(struct fit_handle *handle, struct device_node *sig_node)
+static int fit_verify_signature(struct fit_handle *handle,
+				struct device_node *sig_node,
+				struct device_node *conf_node)
 {
 	uint32_t hashed_strings_start, hashed_strings_size;
 	struct string_list inc_nodes, exc_props;
@@ -329,6 +413,7 @@ static int fit_verify_signature(struct fit_handle *handle, struct device_node *s
 		pr_err("hashed-strings start not found in %pOF\n", sig_node);
 		return -EINVAL;
 	}
+
 	if (of_property_read_u32_index(sig_node, "hashed-strings", 1,
 	    &hashed_strings_size)) {
 		pr_err("hashed-strings size not found in %pOF\n", sig_node);
@@ -338,12 +423,16 @@ static int fit_verify_signature(struct fit_handle *handle, struct device_node *s
 	string_list_init(&inc_nodes);
 	string_list_init(&exc_props);
 
-	if (of_read_string_list(sig_node, "hashed-nodes", &inc_nodes)) {
-		pr_err("hashed-nodes property not found in %pOF\n", sig_node);
-		ret = -EINVAL;
+	ret = fit_config_build_hash_nodes(handle, conf_node, &inc_nodes);
+	if (ret) {
+		pr_err("Failed to build hash node list for %pOF\n", conf_node);
 		goto out_sl;
 	}
 
+	ret = fit_config_check_hash_nodes(sig_node, &inc_nodes);
+	if (ret)
+		goto out_sl;
+
 	string_list_add(&exc_props, "data");
 
 	digest = fit_alloc_digest(sig_node, &algo);
@@ -738,7 +827,7 @@ int fit_config_verify_signature(struct fit_handle *handle, struct device_node *c
 		if (handle->verbose)
 			of_print_nodes(sig_node, 0, ~0);
 
-		ret = fit_verify_signature(handle, sig_node);
+		ret = fit_verify_signature(handle, sig_node, conf_node);
 		if (ret < 0)
 			return ret;
 	}
-- 
2.47.3