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

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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@xxxxxxxxxxxxxxx> # 5.10.x
Signed-off-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>
---
 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").

Thanks,
Stefano

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