Re: [PATCH] kobject_uevent: Fix OOB access within zap_modalias_env()

[Greg KH]

On Fri, May 24, 2024 at 12:20:03PM +0800, Zijun Hu wrote:
> zap_modalias_env() wrongly calculates size of memory block
> to move, so maybe cause OOB memory access issue, fixed by
> correcting size to memmove.

"maybe" or "does"?  That's a big difference :)

> 
> Fixes: 9b3fa47d4a76 ("kobject: fix suppressing modalias in uevents delivered over netlink")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Zijun Hu <quic_zijuhu@xxxxxxxxxxx>
> ---
>  lib/kobject_uevent.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/lib/kobject_uevent.c b/lib/kobject_uevent.c
> index 03b427e2707e..f153b4f9d4d9 100644
> --- a/lib/kobject_uevent.c
> +++ b/lib/kobject_uevent.c
> @@ -434,7 +434,7 @@ static void zap_modalias_env(struct kobj_uevent_env *env)
>  
>  		if (i != env->envp_idx - 1) {
>  			memmove(env->envp[i], env->envp[i + 1],
> -				env->buflen - len);
> +				env->buf + env->buflen - env->envp[i + 1]);

How is this "more correct"?  Please explain it better, this logic is not
obvious at all.

thanks,

greg k-h