netdev - Re: [patch 2/2] [PATCH] qeth: l3 hw tx csum circumvent hw bug

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Message-Id: <20110112.234735.160088590.davem@davemloft.net>
Date:	Wed, 12 Jan 2011 23:47:35 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	frank.blaschka@...ibm.com
Cc:	netdev@...r.kernel.org, linux-s390@...r.kernel.org
Subject: Re: [patch 2/2] [PATCH] qeth: l3 hw tx csum circumvent hw bug

From: frank.blaschka@...ibm.com
Date: Thu, 13 Jan 2011 07:42:25 +0100

> --- a/drivers/s390/net/qeth_l3_main.c
> +++ b/drivers/s390/net/qeth_l3_main.c
> @@ -2998,7 +2998,9 @@ static inline void qeth_l3_hdr_csum(stru
>  	 */
>  	if (iph->protocol == IPPROTO_UDP)
>  		hdr->hdr.l3.ext_flags |= QETH_HDR_EXT_UDP;
> -	hdr->hdr.l3.ext_flags |= QETH_HDR_EXT_CSUM_TRANSP_REQ;
> +	hdr->hdr.l3.ext_flags |= QETH_HDR_EXT_CSUM_TRANSP_REQ |
> +		QETH_HDR_EXT_CSUM_HDR_REQ;
> +	iph->check = 0;
>  	if (card->options.performance_stats)
>  		card->perf_stats.tx_csum++;
>  }

You may not change the packet header contents blindly like this.
Otherwise unpredictable contents will be seen by tcpdump and any
other code path which has a clone of this packet.

Thus, you'll need to guard this change with something like:

		if (skb_header_cloned(skb) &&
		    pskb_expand_head(skb, 0, 0, GFP_ATOMIC)) {
			dev_kfree_skb(skb);
			goto tx_fail;
		}

Please fix this and resubmit your two patches.
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