Re: [PATCH] net/virtio-user: fix cannot get initialized

["Tan, Jianfeng" <jianfeng.tan@intel.com>]

On 4/13/2017 10:21 AM, Yuanhan Liu wrote:
> On Thu, Apr 13, 2017 at 10:18:43AM +0800, Tan, Jianfeng wrote:
>>
>> On 4/13/2017 9:58 AM, Yuanhan Liu wrote:
>>> On Fri, Apr 07, 2017 at 07:57:40AM +0000, Jianfeng Tan wrote:
>>>> After the introduction of vhost MTU, VIRTIO_NET_F_MTU is enabled
>>>> by default. However, virtio-user vtpci does not support to get
>>>> MTU from device yet, i.e., vtpci_read_dev_config(MTU) fails.
>>>> Plus, struct virtio_net_config is defined as a uninitialized
>>>> variable, and could be different values in
>>>> virtio_negotiate_features() and virtio_init_device().
>>>>
>>>> In some cases, it passes the check in virtio_negotiate_features()
>>>> but fails the check in virtio_init_device(). As a result,
>>>> virtio-user canno be initialized.
>>>>
>>>> To fix it, (1) accessing uninitialized variable is not a good
>>>> practice, so initialize it as zero; (2) explicitly disable MTU
>>>> feature in virtio-user.
>>>>
>>>> Fixes: 49d26d9e3f47 ("net/virtio: support MTU feature")
>>>> Cc: Maxime Coquelin <maxime.coquelin@redhat.com>
>>>> Cc: Yuanhan Liu <yuanhan.liu@linux.intel.com>
>>>>
>>>> Signed-off-by: Jianfeng Tan <jianfeng.tan@intel.com>
>>>> ---
>>>>   drivers/net/virtio/virtio_ethdev.c               | 4 ++--
>>>>   drivers/net/virtio/virtio_user/virtio_user_dev.c | 6 ++++++
>>>>   2 files changed, 8 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/net/virtio/virtio_ethdev.c b/drivers/net/virtio/virtio_ethdev.c
>>>> index 78cb3e8..4c43784 100644
>>>> --- a/drivers/net/virtio/virtio_ethdev.c
>>>> +++ b/drivers/net/virtio/virtio_ethdev.c
>>>> @@ -1163,7 +1163,7 @@ virtio_negotiate_features(struct virtio_hw *hw, uint64_t req_features)
>>>>   	/* If supported, ensure MTU value is valid before acknowledging it. */
>>>>   	if (host_features & req_features & (1ULL << VIRTIO_NET_F_MTU)) {
>>>> -		struct virtio_net_config config;
>>>> +		struct virtio_net_config config = {0};
>>> virtio-user does not support the MTU feature, this patch should not be
>>> reached. The virtio-user feature negotiation should be broken.
>>>
>>> 	--yliu
>>>
>> Yes, it will not come to here anyway. But some static code analyzer might
>> report this as an error: there's chance to read uninitialized variable.
> If so, fix it in another patch, with the detailed (and real) errors in
> the commit log.
>

OK, I'll drop this fix from this patch.