[PATCH v2 3/4] bootconfig: Skip internal tree sanity checks in kernel

[Masami Hiramatsu (Google)]

From: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>

In xbc_verify_tree(), the loop iterating through all nodes to check that
xbc_nodes[i].next < xbc_node_num and xbc_nodes[i].child < xbc_node_num
is a defensive sanity check against implementation regressions (such
an out-of-bounds index cannot be produced by malformed input).

Running this check in the kernel adds unnecessary boot-time overhead.
Split this check out into xbc_sanity_check_tree() for userspace, so
that it continues to run during userspace bootconfig validation (e.g.
when applying or testing bootconfig with tools/bootconfig), but is
omitted in the kernel to speed up initialization.

Reported-by: Sang-Heon Jeon <ekffu200098@xxxxxxxxx>
Closes: https://lore.kernel.org/all/20260905141637.1547429-1-ekffu200098@xxxxxxxxx/
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
Reviewed-by: Sang-Heon Jeon <ekffu200098@xxxxxxxxx>
---
 lib/bootconfig.c |   38 ++++++++++++++++++++++++++------------
 1 file changed, 26 insertions(+), 12 deletions(-)

diff --git a/lib/bootconfig.c b/lib/bootconfig.c
index 61cae6d6e3f8..20b3d6e78fea 100644
--- a/lib/bootconfig.c
+++ b/lib/bootconfig.c
@@ -1003,9 +1003,30 @@ static int __init xbc_close_brace(char **k, char *n)
 	return __xbc_close_brace(n - 1);
 }
 
+#ifndef __KERNEL__
+/* Sanity check for regression: node indices must be within bounds */
+static int __init xbc_sanity_check_tree(void)
+{
+	int i;
+
+	for (i = 0; i < xbc_node_num; i++) {
+		if (xbc_nodes[i].next >= xbc_node_num) {
+			return xbc_parse_error("No closing brace",
+				xbc_node_get_data(xbc_nodes + i));
+		}
+		if (xbc_nodes[i].child >= xbc_node_num) {
+			return xbc_parse_error("Broken child node",
+				xbc_node_get_data(xbc_nodes + i));
+		}
+	}
+
+	return 0;
+}
+#endif
+
 static int __init xbc_verify_tree(void)
 {
-	int i, depth;
+	int depth;
 	size_t len, wlen;
 	struct xbc_node *n, *m;
 
@@ -1022,17 +1043,6 @@ static int __init xbc_verify_tree(void)
 		return -ENOENT;
 	}
 
-	for (i = 0; i < xbc_node_num; i++) {
-		if (xbc_nodes[i].next >= xbc_node_num) {
-			return xbc_parse_error("No closing brace",
-				xbc_node_get_data(xbc_nodes + i));
-		}
-		if (xbc_nodes[i].child >= xbc_node_num) {
-			return xbc_parse_error("Broken child node",
-				xbc_node_get_data(xbc_nodes + i));
-		}
-	}
-
 	/* Key tree limitation check */
 	n = &xbc_nodes[0];
 	depth = 1;
@@ -1203,6 +1213,10 @@ int __init xbc_init(const char *data, size_t size, const char **emsg, int *epos)
 	ret = xbc_parse_tree();
 	if (!ret)
 		ret = xbc_verify_tree();
+#ifndef __KERNEL__
+	if (!ret)
+		ret = xbc_sanity_check_tree();
+#endif
 
 	if (ret < 0) {
 		if (epos)