linux-kernel - Re: [PATCH v2] nbd_genl_status: null check for nla_nest

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Date:   Tue, 10 Sep 2019 13:35:21 +0200
From:   Michal Kubecek <mkubecek@...e.cz>
To:     Navid Emamdoost <navid.emamdoost@...il.com>
Cc:     josef@...icpanda.com, kjlu@....edu, smccaman@....edu,
        secalert@...hat.com, emamd001@....edu,
        Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org,
        nbd@...er.debian.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] nbd_genl_status: null check for nla_nest_start

(Just stumbled upon this patch when link to it came with a CVE bug report.)

On Mon, Jul 29, 2019 at 11:42:26AM -0500, Navid Emamdoost wrote:
> nla_nest_start may fail and return NULL. The check is inserted, and
> errno is selected based on other call sites within the same source code.
> Update: removed extra new line.
> 
> Signed-off-by: Navid Emamdoost <navid.emamdoost@...il.com>
> Reviewed-by: Bob Liu <bob.liu@...cle.com>
> ---
>  drivers/block/nbd.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
> index 9bcde2325893..2410812d1e82 100644
> --- a/drivers/block/nbd.c
> +++ b/drivers/block/nbd.c
> @@ -2149,6 +2149,11 @@ static int nbd_genl_status(struct sk_buff *skb, struct genl_info *info)
>  	}
>  
>  	dev_list = nla_nest_start_noflag(reply, NBD_ATTR_DEVICE_LIST);
> +	if (!dev_list) {
> +		ret = -EMSGSIZE;
> +		goto out;
> +	}
> +
>  	if (index == -1) {
>  		ret = idr_for_each(&nbd_index_idr, &status_cb, reply);
>  		if (ret) {

You should also call nlmsg_free(reply) when you bail out so that you
don't introduce a memory leak.

Michal Kubecek