linux-kernel - Re: [PATCH V4 5/6] net: maclorawan: Implement maclorawan class module

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Message-ID: <20181204204508.3ebead06@alans-desktop>
Date:   Tue, 4 Dec 2018 20:45:08 +0000
From:   Alan Cox <gnomes@...rguk.ukuu.org.uk>
To:     Jian-Hong Pan <starnight@...cu.edu.tw>
Cc:     Andreas Färber <afaerber@...e.de>,
        "David S . Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Marcel Holtmann <marcel@...tmann.org>,
        Dollar Chen <dollar.chen@...ec.com>,
        Ken Yu <ken.yu@...wireless.com>, linux-wpan@...r.kernel.org,
        Stefan Schmidt <stefan@...enfreihafen.org>
Subject: Re: [PATCH V4 5/6] net: maclorawan: Implement maclorawan class
 module

> +void
> +lrw_parse_frame(struct lrw_session *ss, struct sk_buff *skb)
> +{
> +	struct lrw_fhdr *fhdr = &ss->rx_fhdr;
> +	__le16 *p_fcnt;
> +
> +	pr_debug("%s: %s\n", LORAWAN_MODULE_NAME, __func__);
> +
> +	/* Get message type */
> +	fhdr->mtype = skb->data[0];
> +	skb_pull(skb, LRW_MHDR_LEN);

This does not seem robust. There is no point at which you actually check
the message size is valid etc

> +	fhdr->fopts_len = fhdr->fctrl & 0xF;
> +	if (fhdr->fopts_len > 0) {
> +		memcpy(fhdr->fopts, skb->data, fhdr->fopts_len);
> +		skb_pull(skb, fhdr->fopts_len);
> +	}

In fact you appear to copy random kernel memory into a buffer
> +
> +	/* TODO: Parse frame options */
> +
> +	/* Remove message integrity code */
> +	skb_trim(skb, skb->len - LRW_MIC_LEN);

and then try and trim the buffer to a negative size ?

Alan