Re: [PATCH v2] audit: fix potential null dereference 'context->module.name'
From: Paul Moore
Date: Mon Jul 30 2018 - 19:04:34 EST
On Tue, Jul 24, 2018 at 10:28 PM Yi Wang <wang.yi59@xxxxxxxxxx> wrote:
> The variable 'context->module.name' may be null pointer when
> kmalloc return null, so it's better to check it before using
> to avoid null dereference.
> Another one more thing this patch does is using kstrdup instead
> of (kmalloc + strcpy), and signal a lost record via audit_log_lost.
>
> Signed-off-by: Yi Wang <wang.yi59@xxxxxxxxxx>
> Reviewed-by: Jiang Biao <jiang.biao2@xxxxxxxxxx>
> ---
> v2: use kstrdup instead of kmalloc + strcpy, and signal a lost
> record. Thanks to Eric and Paul.
>
> kernel/auditsc.c | 13 +++++++++----
> 1 file changed, 9 insertions(+), 4 deletions(-)
Thanks, this looks good to me. I'm also going to tag this for -stable.
I'm building a test kernel right now and if all goes well I'll send
this up to Linus for v4.18; if he doesn't pull it for v4.18 I'll add
this to the audit/next branch.
> diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> index e80459f..713386a 100644
> --- a/kernel/auditsc.c
> +++ b/kernel/auditsc.c
> @@ -1272,8 +1272,12 @@ static void show_special(struct audit_context *context, int *call_panic)
> break;
> case AUDIT_KERN_MODULE:
> audit_log_format(ab, "name=");
> - audit_log_untrustedstring(ab, context->module.name);
> - kfree(context->module.name);
> + if (context->module.name) {
> + audit_log_untrustedstring(ab, context->module.name);
> + kfree(context->module.name);
> + } else
> + audit_log_format(ab, "(null)");
> +
> break;
> }
> audit_log_end(ab);
> @@ -2408,8 +2412,9 @@ void __audit_log_kern_module(char *name)
> {
> struct audit_context *context = current->audit_context;
>
> - context->module.name = kmalloc(strlen(name) + 1, GFP_KERNEL);
> - strcpy(context->module.name, name);
> + context->module.name = kstrdup(name, GFP_KERNEL);
> + if (!context->module.name)
> + audit_log_lost("out of memory in __audit_log_kern_module");
> context->type = AUDIT_KERN_MODULE;
> }
>
> --
> 1.8.3.1
>
--
paul moore
www.paul-moore.com