netdev - Re: [PATCH RFC 1/2] net/802: Implement Multiple Registration Protocol (MRP)

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Date:	Mon, 24 Sep 2012 23:36:48 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Ward <david.ward@...mit.edu>
Cc:	netdev@...r.kernel.org, Patrick McHardy <kaber@...sh.net>,
	Philip Foulkes <philip.foulkes@...il.com>
Subject: Re: [PATCH RFC 1/2] net/802: Implement Multiple Registration
 Protocol (MRP)

On Mon, 2012-09-24 at 17:07 -0400, David Ward wrote:

...

> +static int mrp_pdu_parse_end_mark(struct sk_buff *skb)
> +{
> +	__be16 *endmark;
> +
> +	if (!pskb_may_pull(skb, sizeof(*endmark)))
> +		return -1;
> +	endmark = (__be16 *)skb->data;
> +	if (get_unaligned(endmark) == MRP_END_MARK) {

You might try get_unaligned_be16(skb->data) ...

> +		skb_pull(skb, sizeof(*endmark));
> +		return -1;
> +	}
> +	return 0;
> +}
> +

...

> +
> +static int mrp_pdu_parse_msg(struct mrp_applicant *app, struct sk_buff *skb)
> +{
> +	if (!pskb_may_pull(skb, sizeof(*mrp_cb(skb)->mh)))
> +		return -1;
> +	mrp_cb(skb)->mh = (struct mrp_msg_hdr *)skb->data;

here you store a pointer to skb->data, in skb>cb[]

> +	if (mrp_cb(skb)->mh->attrtype == 0 ||
> +	    mrp_cb(skb)->mh->attrtype > app->app->maxattr ||
> +	    mrp_cb(skb)->mh->attrlen == 0)
> +		return -1;
> +	if (sizeof(struct mrp_skb_cb) + mrp_cb(skb)->mh->attrlen >
> +	    FIELD_SIZEOF(struct sk_buff, cb))
> +		return -1;
> +	skb_pull(skb, sizeof(*mrp_cb(skb)->mh));
> +
> +	while (skb->len > 0) {
> +		if (mrp_pdu_parse_end_mark(skb) < 0)
> +			break;

but skb->head can be reallocated by other pskb_may_pull() calls
done in mrp_pdu_parse_end_mark() (and elsewhere)

So skb->cb[] might contain a pointer to a freed memory.

> +		if (mrp_pdu_parse_vecattr(app, skb) < 0)
> +			return -1;
> +	}
> +	return 0;
> +}
> +

You might consider using skb_header_pointer() instead of
pskb_may_pull()/skb_pull(), it might be easier when you have such nested
headers...



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