[PATCH net-next v5] net/ncsi: Extend NC-SI Netlink interface to allow user space to send NC-SI command

[Samuel Mendoza-Jonas]

On Wed, 2018-10-10 at 18:11 +0000, Justin.Lee1 at Dell.com wrote:
<snip>
> +
> +	len = nla_len(info->attrs[NCSI_ATTR_DATA]);
> +	if (len < sizeof(struct ncsi_pkt_hdr)) {
> +		netdev_info(ndp->ndev.dev, "NCSI: no command to send %u\n",
> +			    package_id);
> +		ret = -EINVAL;
> +		goto out_netlink;
> +	} else {
> +		data = (unsigned char *)nla_data(info->attrs[NCSI_ATTR_DATA]);
> +	}

I only just noticed this, the call to nla_len() can cause a null-dereference if
the NCSI_ATTR_DATA attribute isn't present; we need to make sure it exists
before accessing it in info->attrs.

eg:

root at ozrom2-bmc:~# ./ncsi-netlink -l 2 -p 0 -c 0 --cmd
[   81.399837] Unable to handle kernel NULL pointer dereference at virtual address 00000000
[   81.409092] pgd = ddaa9fa6
[   81.413084] [00000000] *pgd=9702c831, *pte=00000000, *ppte=00000000
[   81.420729] Internal error: Oops: 17 [#1] ARM
[   81.426447] CPU: 0 PID: 1028 Comm: ncsi-netlink Not tainted 4.18.8-sammj-00144-gbc129f31bfa5 #12
...
[   81.874434] Kernel panic - not syncing: Fatal exception

Cheers,
Sam