On Fri, Aug 15, 2025 at 09:19:34PM +0200, Alyssa Ross wrote: > Alyssa Ross <hi@xxxxxxxxx> writes: > > > 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 > > Okay, just found that it's already been reverted: > https://lore.kernel.org/all/20250808072533-mutt-send-email-mst@xxxxxxxxxx/ > > Still, I'm confused how this was supposed to fix anything… > > #regzbot fix: Revert "virtio: reject shm region if length is zero" Are you asking why was the patch applied in the 1st place? It seemed like an invalid behaviour to me, and I thought it's not too late to block it so we don't need to support it down the road. -- MST
