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:

quoted

On Mon, Feb 15, 2021 at 03:32:19PM +0100, Greg KH wrote:

quoted

On Thu, Feb 11, 2021 at 05:25:19PM +0100, Stefano Garzarella wrote:

quoted

Commit 65b709586e222fa6ffd4166ac7fdb5d5dad113ee upstream.

No, this really is not that commit, so please do not say it is.

Oops, sorry.

quoted

quoted

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: <redacted> # 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