linux-kernel - Re: [PATCH] audit: fix potential null dereference 'context->module.name'

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Message-ID: <450ab68cc6b7cebbf1b6292e3140932ea1ac9e57.camel@redhat.com>
Date:   Tue, 24 Jul 2018 07:39:31 -0400
From:   Eric Paris <eparis@...hat.com>
To:     Yi Wang <wang.yi59@....com.cn>, paul@...l-moore.com
Cc:     linux-audit@...hat.com, linux-kernel@...r.kernel.org,
        jiang.biao2@....com.cn, zhong.weidong@....com.cn
Subject: Re: [PATCH] audit: fix potential null dereference
 'context->module.name'

Would it make more sense to actually check for failure on allocation
rather than try to remember to deal with it later? How about we just
have audit_log_kern_module return an error and fail if we are OOM?
(also this seems like a good place to use kstrdup, instead of
kmalloc+strcpy)

On Tue, 2018-07-24 at 13:57 +0800, Yi Wang 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.
> 
> Signed-off-by: Yi Wang <wang.yi59@....com.cn>
> Reviewed-by: Jiang Biao <jiang.biao2@....com.cn>
> ---
>  kernel/auditsc.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> index e80459f..4830b83 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);
> @@ -2409,7 +2413,8 @@ 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);
> +	if (context->module.name)
> +		strcpy(context->module.name, name);
>  	context->type = AUDIT_KERN_MODULE;
>  }
>