netdev - Re: [PATCH net] xen-netback: disable rogue vif in kthread context

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Date:	Mon, 24 Mar 2014 12:22:04 +0000
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	Wei Liu <wei.liu2@...rix.com>
CC:	<netdev@...r.kernel.org>, <xen-devel@...ts.xen.org>,
	<paul.durrant@...rix.com>, <zoltan.kiss@...rix.com>,
	<edwin@...rok.net>
Subject: Re: [PATCH net] xen-netback: disable rogue vif in kthread context

On Mon, 2014-03-24 at 12:13 +0000, Wei Liu wrote:
> When netback discovers frontend is sending malformed packet it will
> disables the interface which serves that frontend.
> 
> However disabling a network interface involving taking a mutex which
> cannot be done in softirq context, so we need to defer this process to
> kthread context.
> 
> This patch does the following:
> 1. introduce a flag to indicate the interface is disabled.
> 2. check that flag in TX path, don't do any work if it's true.
> 3. check that flag in RX path, turn off that interface if it's true.
> 
> The reason to disable it in RX path is because RX uses kthread. After
> this change the behavior of netback is still consistent -- it won't do
> any TX work for a rogue frontend, and the interface will be eventually
> turned off.
> 
> Also change a "continue" to "break" after xenvif_fatal_tx_err, as it
> doesn't make sense to continue processing packets if frontend is rogue.
> 
> This is a fix for XSA-90.
> 
> Reported-by: Török Edwin <edwin@...rok.net>
> Signed-off-by: Wei Liu <wei.liu2@...rix.com>

Acked-by: Ian Campbell <ian.campbell@...rix.com>

> +		if (unlikely(vif->disabled) && netif_carrier_ok(vif->dev))

Perhaps consider extending the scope of the unlikely over the entire
expression? (not that I expect it will matter much)

Ian.

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