netdev - Re: [PATCH] tun: fix BUG with large packets without TUN_VNET

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Message-ID: <20090416235023.GC29988@gondor.apana.org.au>
Date:	Fri, 17 Apr 2009 07:50:23 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	"Michael S. Tsirkin" <m.s.tsirkin@...il.com>
Cc:	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	Max Krasnyansky <maxk@...lcomm.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: [PATCH] tun: fix BUG with large packets without TUN_VNET_HDR

On Thu, Apr 16, 2009 at 11:45:57PM +0300, Michael S. Tsirkin wrote:
> On a tap device, the linear part of skb must be at least ETH_HLEN,
> otherwise eth_type_trans triggers BUG_ON in skb_pull(skb, ETH_HLEN).
> This patch makes sure the linear part is always large enough.
> 
> Without the patch, tun sets the linear part size to 0 if TUN_VNET_HDR
> is not set and the packet is too large to put in a linear skb,
> which causes BUGs for me.
> 
> BTW, it seems that this behaviour has been there for a long while, since at
> least v2.6.27 (commit f42157cb568c1eb02eca7df4da67553a9edae24a: tun: fallback
> if skb_alloc() fails on big packets), but started triggering for me only in
> v2.6.30-rc1, because of commit 33dccbb050bbe35b88ca8cf1228dcf3e4d4b3554 (tun:
> Limit amount of queued packets per device), which made all large packets
> non-linear.  Before that, most packets would still typically be linear until
> memory gets fragmented, which hides the issue.
> 
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>

I'd already fixed that a couple of days ago :)
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