Re: [PATCH v4 08/17] lib/bootconfig: fix off-by-one in xbc_verify_tree() next node check

[Masami Hiramatsu (Google) <mhiramat@kernel.org>]

On Sat, 14 Mar 2026 23:01:46 +0000
Josh Law <objecting@objecting.org> wrote:

> Valid node indices are 0 to xbc_node_num-1, so a next value equal to
> xbc_node_num is out of bounds.  Use >= instead of > to catch this.
> 
> A malformed or corrupt bootconfig could pass tree verification with
> an out-of-bounds next index.  On subsequent tree traversal at boot
> time, xbc_node_get_next() would return a pointer past the allocated
> xbc_nodes array, causing an out-of-bounds read of kernel memory.
> 

Thanks, but How? Do you have any actual config example?
Unless that, I would like to treat this as a minor fix.

Thanks,

> Signed-off-by: Josh Law <objecting@objecting.org>
> ---
>  lib/bootconfig.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/lib/bootconfig.c b/lib/bootconfig.c
> index 58d6ae297280..56fbedc9e725 100644
> --- a/lib/bootconfig.c
> +++ b/lib/bootconfig.c
> @@ -816,7 +816,7 @@ static int __init xbc_verify_tree(void)
>  	}
>  
>  	for (i = 0; i < xbc_node_num; i++) {
> -		if (xbc_nodes[i].next > xbc_node_num) {
> +		if (xbc_nodes[i].next >= xbc_node_num) {
>  			return xbc_parse_error("No closing brace",
>  				xbc_node_get_data(xbc_nodes + i));
>  		}
> -- 
> 2.34.1
> 


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