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

- From: Masami Hiramatsu (Google) \<mhiramat@kernel.org\>
- Date: 2026-11-05 12:24:03 
- List: linux-trace-kernel
- Page: https://ratatoskr.run/linux-trace-kernel/2026/11/17870291
- Thread: https://ratatoskr.run/linux-trace-kernel/2026/11/17858716/t.md

```text
On Wed,  4 Nov 2026 15:37:41 +0800, Zhiqi Zhang [ref] wrote:
> 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.

Ah, good catch! Let me pick it.

Thank you!

>
> 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: <redacted>
> Signed-off-by: Zhiqi Zhang <redacted>
> ---
>  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)
>

-- 
Masami Hiramatsu (Google) [ref]

```