On Mon, May 12, 2025 at 07:51:53AM +0930, SamiUddinsami.md.ko@xxxxxxxxx wrote: > From: Sami Uddin <sami.md.ko@xxxxxxxxx> > > Prevent usage of shared memory regions where the length is zero, > as such configurations are not valid and may lead to unexpected behavior. > > Signed-off-by: Sami Uddin <sami.md.ko@xxxxxxxxx> > --- > v3: > - Use idiomatic 'if (!region->len)' as suggested by reviewer > v2: > - Fixed coding style issue: added space after 'if' statement > > include/linux/virtio_config.h | 2 ++ > 1 file changed, 2 insertions(+) Hi, I'm sorry to be the bearer of bad news, but since this patch my VM no longer works. The system is running wayland-proxy-virtwl[1] inside a crosvm[2] VM, using crosvm's virtio-gpu device to do cross-domain Wayland forwarding. Since this change, wayland-proxy-virtwl crashes with the following log message: wl-proxy [WARNING]: Error handling client: Unix.Unix_error(Unix.EINVAL, "DRM_IOCTL_VIRTGPU_RESOURCE_CREATE_BLOB", "") I'm pretty confused by what this change was supposed to do in the first place… Looking at how virtio_get_shm_region() is used in virtio_gpu_init(), it's called with a pointer to zeroed memory, and then the get_shm_region() implementation is supposed to write to the region, without ever reading from it as far as I can tell. Why is the initial value of an out parameter being checked at all? How does this prevent using zero-length shared memory regions? [1]: https://crosvm.dev/ [2]: https://github.com/talex5/wayland-proxy-virtwl #regzbot introduced: 206cc44588f72b49ad4d7e21a7472ab2a72a83df > diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h > index 169c7d367fac..b3e1d30c765b 100644 > --- a/include/linux/virtio_config.h > +++ b/include/linux/virtio_config.h > @@ -329,6 +329,8 @@ static inline > bool virtio_get_shm_region(struct virtio_device *vdev, > struct virtio_shm_region *region, u8 id) > { > + if (!region->len) > + return false; > if (!vdev->config->get_shm_region) > return false; > return vdev->config->get_shm_region(vdev, region, id); > -- > 2.34.1 >
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