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SubjectRE: [PATCH 4/4] hyperv: netvsc: improve protection against rescind offer
Date
> -----Original Message-----
> From: Vitaly Kuznetsov [mailto:vkuznets@redhat.com]
> Sent: Wednesday, February 4, 2015 1:01 AM
> To: KY Srinivasan; devel@linuxdriverproject.org
> Cc: Haiyang Zhang; linux-kernel@vger.kernel.org; Dexuan Cui; Jason Wang
> Subject: [PATCH 4/4] hyperv: netvsc: improve protection against rescind offer
>
> The check added in commit c3582a2c4d0b ("hyperv: Add support for vNIC hot
> removal") is incomplete as there is no synchronization between
> vmbus_onoffer_rescind() and netvsc_send(). In case we get the offer after we
> checked out_channel->rescind and before netvsc_send() finishes its job we can
> get a crash as we'll be dealing with already freed channel.
>
> Make netvsc_send() take additional reference to the channel with newly
> introduced vmbus_get_channel(), this guarantees we won't lose the channel.
> We
> can still get rescind while we're processing but this won't cause a crash.
>
> Reported-by: Jason Wang <jasowang@redhat.com>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
> drivers/net/hyperv/netvsc.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/hyperv/netvsc.c b/drivers/net/hyperv/netvsc.c
> index 9f49c01..d9b13a1 100644
> --- a/drivers/net/hyperv/netvsc.c
> +++ b/drivers/net/hyperv/netvsc.c
> @@ -763,11 +763,16 @@ int netvsc_send(struct hv_device *device,
> out_channel = net_device->chn_table[packet->q_idx];
> if (out_channel == NULL)
> out_channel = device->channel;
> - packet->channel = out_channel;
> + packet->channel = vmbus_get_channel(out_channel);
>
> - if (out_channel->rescind)
> + if (!packet->channel)
> return -ENODEV;
>
> + if (out_channel->rescind) {
> + vmbus_put_channel(out_channel);

IMO the patch doesn't resolve the real issue.
At most it prevents the channel from disappearing in netvsc_send() only,
while actually we also need to make sure the channel is not freed before the
driver runs netvsc_remove() -> rndis_filter_device_remove() ->
-> netvsc_device_remove() -> vmbus_close().

I suggest we add vmbus_get/put_channel() in vmbus_open/close()?

-- Dexuan

> + return -ENODEV;
> + }
> +
> if (packet->page_buf_cnt) {
> ret = vmbus_sendpacket_pagebuffer(out_channel,
> packet->page_buf,
> @@ -810,6 +815,7 @@ int netvsc_send(struct hv_device *device,
> packet, ret);
> }
>
> + vmbus_put_channel(packet->channel);
> return ret;
> }
>
> --



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