[PATCH 1/2] bootconfig: Allow keys with the maximum supported depth

[Zhiqi Zhang]

xbc_verify_tree() accepts keys with XBC_DEPTH_MAX (16) components,
but xbc_node_compose_key_after() returns -ERANGE immediately after
storing the sixteenth component. It rejects the key before discovering
that there are no more ancestors to collect.

For example, a.b.c.d.e.f.g.h.i.j.k.l.m.n.o.p = value can be attached
to an initrd successfully. However, bootconfig -l stops listing and
prints "Failed to compose key -34". In the kernel, the same error
propagates through copy_xbc_key_value_list() during its length probe,
so proc_boot_config_init() returns before creating /proc/bootconfig.

Check the array capacity before storing the next component. This lets
exactly XBC_DEPTH_MAX components be composed while retaining the check
before any out-of-bounds store.

I found this issue while reviewing bootconfig's depth handling and used
OpenAI Codex to verify the failure and develop the fix. I reviewed the
change and wrote and ran the regression tests.

Fixes: 76db5a27a827 ("bootconfig: Add Extra Boot Config support")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Zhiqi Zhang <zhiqizhangg@xxxxxxxxx>
---
 lib/bootconfig.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/bootconfig.c b/lib/bootconfig.c
index 819685d6c68d..a4aae9a9abca 100644
--- a/lib/bootconfig.c
+++ b/lib/bootconfig.c
@@ -428,9 +428,9 @@ int __init xbc_node_compose_key_after(struct xbc_node *root,
 		node = xbc_node_get_parent(node);
 
 	while (node && node != root) {
-		keys[depth++] = xbc_node_index(node);
 		if (depth == XBC_DEPTH_MAX)
 			return -ERANGE;
+		keys[depth++] = xbc_node_index(node);
 		node = xbc_node_get_parent(node);
 	}
 	if (!node && root)
-- 
2.54.0 (Apple Git-157)