Re: [PATCH for 5.10] vdpa_sim: fix param validation in vdpasim_get_config()

[Stefano Garzarella <sgarzare@redhat.com>]

On Mon, Feb 15, 2021 at 04:23:54PM +0100, Greg KH wrote:
>On Mon, Feb 15, 2021 at 04:03:21PM +0100, Stefano Garzarella wrote:
>> On Mon, Feb 15, 2021 at 03:32:19PM +0100, Greg KH wrote:
>> > On Thu, Feb 11, 2021 at 05:25:19PM +0100, Stefano Garzarella wrote:
>> > > Commit 65b709586e222fa6ffd4166ac7fdb5d5dad113ee upstream.
>> >
>> > No, this really is not that commit, so please do not say it is.
>>
>> Oops, sorry.
>>
>> >
>> > > Before this patch, if 'offset + len' was equal to
>> > > sizeof(struct virtio_net_config), the entire buffer wasn't filled,
>> > > returning incorrect values to the caller.
>> > >
>> > > Since 'vdpasim->config' type is 'struct virtio_net_config', we can
>> > > safely copy its content under this condition.
>> > >
>> > > Commit 65b709586e22 ("vdpa_sim: add get_config callback in
>> > > vdpasim_dev_attr") unintentionally solved it upstream while
>> > > refactoring vdpa_sim.c to support multiple devices. But we don't want
>> > > to backport it to stable branches as it contains many changes.
>> > >
>> > > Fixes: 2c53d0f64c06 ("vdpasim: vDPA device simulator")
>> > > Cc: <stable@vger.kernel.org> # 5.10.x
>> > > Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
>> > > ---
>> > >  drivers/vdpa/vdpa_sim/vdpa_sim.c | 2 +-
>> > >  1 file changed, 1 insertion(+), 1 deletion(-)
>> > >
>> > > diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.c b/drivers/vdpa/vdpa_sim/vdpa_sim.c
>> > > index 6a90fdb9cbfc..8ca178d7b02f 100644
>> > > --- a/drivers/vdpa/vdpa_sim/vdpa_sim.c
>> > > +++ b/drivers/vdpa/vdpa_sim/vdpa_sim.c
>> > > @@ -572,7 +572,7 @@ static void vdpasim_get_config(struct vdpa_device *vdpa, unsigned int offset,
>> > >  {
>> > >  	struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
>> > >
>> > > -	if (offset + len < sizeof(struct virtio_net_config))
>> > > +	if (offset + len <= sizeof(struct virtio_net_config))
>> > >  		memcpy(buf, (u8 *)&vdpasim->config + offset, len);
>> > >  }
>> >
>> > I'll be glad to take a one-off patch, but why can't we take the real
>> > upstream patch?  That is always the better long-term solution, right?
>>
>> Because that patch depends on the following patches merged in v5.11-rc1
>> while refactoring vdpa_sim:
>>   f37cbbc65178 vdpa_sim: make 'config' generic and usable for any device type
>>   cf1a3b35382c vdpa_sim: store parsed MAC address in a buffer
>>   a13b5918fdd0 vdpa_sim: add work_fn in vdpasim_dev_attr
>>   011c35bac5ef vdpa_sim: add supported_features field in vdpasim_dev_attr
>>   2f8f46188805 vdpa_sim: add device id field in vdpasim_dev_attr
>>   6c6e28fe4579 vdpa_sim: add struct vdpasim_dev_attr for device attributes
>>   36a9c3063025 vdpa_sim: rename vdpasim_config_ops variables
>>   423248d60d2b vdpa_sim: remove hard-coded virtq count
>>
>> Maybe we can skip some of them, but IMHO should be less risky to apply only
>> this change.
>>
>> If you want I can try to figure out the minimum sub-set of patches needed
>> for 65b709586e22 ("vdpa_sim: add get_config callback in vdpasim_dev_attr").
>
>The minimum is always nice :)
>

The minimum set, including the patch that fixes the issue, is the 
following:

   65b709586e22 vdpa_sim: add get_config callback in vdpasim_dev_attr
   f37cbbc65178 vdpa_sim: make 'config' generic and usable for any device type
   cf1a3b35382c vdpa_sim: store parsed MAC address in a buffer
   6c6e28fe4579 vdpa_sim: add struct vdpasim_dev_attr for device attributes
   423248d60d2b vdpa_sim: remove hard-coded virtq count

The patches apply fairly cleanly. There are a few contextual differences 
due to the lack of the other patches:

   $ git backport-diff -u master -r linux-5.10.y..HEAD
   Key:
   [----] : patches are identical
   [####] : number of functional differences between upstream/downstream patch
   [down] : patch is downstream-only
   The flags [FC] indicate (F)unctional and (C)ontextual differences, respectively

   001/5:[----] [--] 'vdpa_sim: remove hard-coded virtq count'
   002/5:[----] [-C] 'vdpa_sim: add struct vdpasim_dev_attr for device attributes'
   003/5:[----] [--] 'vdpa_sim: store parsed MAC address in a buffer'
   004/5:[----] [-C] 'vdpa_sim: make 'config' generic and usable for any device type'
   005/5:[----] [-C] 'vdpa_sim: add get_config callback in vdpasim_dev_attr'

>If it's just too much churn for no good reason, then yes, the one-line
>change above will be ok, but you need to document the heck out of why
>this is not upstream and that it is a one-off thing.
>

Shortly I'll send the series to stable@vger.kernel.org so you can judge 
if it's okay or better to resend this patch with a better description.

Thanks
Stefano

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