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

From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

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 <redacted>
Closes: https://lore.kernel.org/all/20260905141637.1547429-1-ekffu200098@gmail.com/ (local)
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
 lib/bootconfig.c |   38 ++++++++++++++++++++++++++------------
 1 file changed, 26 insertions(+), 12 deletions(-)

diff --git a/lib/bootconfig.c b/lib/bootconfig.c
index 0ec2874db9c7..884f186b1989 100644
--- a/lib/bootconfig.c
+++ b/lib/bootconfig.c

@@ -1000,9 +1000,30 @@ 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;

@@ -1019,17 +1040,6 @@ 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;

@@ -1199,6 +1209,10 @@ 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)