On Fri, Nov 28, 2025 at 04:28:20PM -0500, Demi Marie Obenour wrote: > On 11/28/25 16:08, Alyssa Ross wrote: > > Demi Marie Obenour writes: > > > >> On 11/28/25 15:41, Alyssa Ross wrote: > >>> Demi Marie Obenour writes: > >>> > >>>> On 11/28/25 08:47, Alyssa Ross wrote: > >>>>> Demi Marie Obenour writes: > >>>>> > >>>>>> diff --git a/host/rootfs/image/usr/bin/spectrum-update b/host/rootfs/image/usr/bin/spectrum-update > >>>>>> new file mode 100755 > >>>>>> index 0000000000000000000000000000000000000000..613b43570d0538fce20296ccb1de2a6364e0df55 > >>>>>> --- /dev/null > >>>>>> +++ b/host/rootfs/image/usr/bin/spectrum-update > >>>>>> @@ -0,0 +1,92 @@ > >>>>>> +#!/bin/execlineb -WS1 > >>>>>> +# SPDX-License-Identifier: EUPL-1.2+ > >>>>>> +# SPDX-FileCopyrightText: 2025 Demi Marie Obenour > >>>>>> + > >>>>>> +if { mkdir -p -m 0700 /run/updater } > >>>>>> + > >>>>>> +# Take a global lock to avoid races. > >>>>>> +s6-setlock /run/update-lock > >>>>>> + > >>>>>> +foreground { redirfd -w 2 /dev/null rmdir -- $1 } > >>>>>> +if { umask 0077 mkdir -p -- $1 } > >>>>>> +cd $1 > >>>>>> +foreground { > >>>>>> + # If this exists already that is okay. > >>>>>> + foreground { redirfd -w 2 /dev/null btrfs subvolume create -- shared } > >>>>>> + > >>>>>> + # Delete any stale temporary files. Delete any existing signature > >>>>>> + # files. If the VM is still running (it should not be), the VM might > >>>>>> + # have write access to the directory. However, updates-dir-check is > >>>>>> + # safe against that. > >>>>>> + if { updates-dir-check cleanup shared } > >>>>>> + > >>>>>> + if { > >>>>>> + foreground { > >>>>>> + # TODO: suppress only "subvolume does not exist" errors. > >>>>>> + redirfd -w 2 /dev/null > >>>>>> + btrfs subvolume delete snapshot > >>>>>> + } > >>>>>> + rm -f snapshot > >>>>>> + } > >>>>>> + > >>>>>> + backtick -E update_vm_id { > >>>>>> + backtick -E id_path { readlink /run/vm/by-name/sys.appvm-systemd-sysupdate } > >>>>>> + basename -- $id_path > >>>>>> + } > >>>>>> + > >>>>>> + # $fsdir is read-only to the guest, but read-write to the host. > >>>>>> + # Directories bind-mounted into it are read-write to the guest. > >>>>>> + # See etc/s6-linux-init/run-image/service/vhost-user-fs/template/run > >>>>>> + # for details. > >>>>>> + > >>>>> > >>>>> This still refers to a non-existent variable. > >> > >> Whoops! > >> > >>>>>> + # Set up /etc with what the VM needs. The VM will overlay this > >>>>>> + # on its own /etc. > >>>>>> + # > >>>>>> + # In the future, this should use a bind mount instead of copying > >>>>>> + # into a tmpfs. However, this would significantly complicate the > >>>>>> + # cleanup code. Deleting fs/etc would require undoing the bind > >>>>>> + # mounts instead of rm -rf. Once this code is in a separate mount > >>>>>> + # namespace, the copies should be replaced by bind mounts. > >>>>>> + if { > >>>>>> + if { rm -rf -- /run/vm/by-id/${update_vm_id}/fs/etc } > >>>>>> + umask 022 > >>>>>> + if { mkdir -p -- /run/vm/by-id/${update_vm_id}/fs/updates /run/vm/by-id/${update_vm_id}/fs/etc/systemd } > >>>>>> + if { cp -R -- /etc/vm-sysupdate.d /etc/update-url /run/vm/by-id/${update_vm_id}/fs/etc } > >>>>>> + cp -- /etc/systemd/import-pubring.gpg /run/vm/by-id/${update_vm_id}/fs/etc/systemd > >>>>>> + } > >>>>>> + > >>>>>> + # If the directory is already mounted, unmount it. This prevents a > >>>>>> + # confusing error from mount. > >>>>>> + foreground { redirfd -w 2 /dev/null umount -- /run/vm/by-id/${update_vm_id}/fs/updates } > >>>>>> + > >>>>>> + # Share the update directory with the VM. > >>>>>> + if { mount --bind -- shared /run/vm/by-id/${update_vm_id}/fs/updates } > >>>>>> + > >>>>>> + # Start the update VM. > >>>>>> + if { vm-start $update_vm_id } > >>>>>> + > >>>>>> + # Wait for the VM to exit. > >>>>>> + # TODO: This is racy. If the update finishes before this code runs, > >>>>>> + # the s6-svwait call will fail. > >>>>>> + if { s6-svwait -D /run/service/vmm/instance/${update_vm_id} } > >>>>>> + > >>>>>> + # Remove the bind mount. > >>>>>> + if { umount -- /run/vm/by-id/${update_vm_id}/fs/updates } > >>>>>> + > >>>>>> + # Ensure that the VM cannot change the directory > >>>>>> + # while systemd-sysupdate is using it. > >>>>>> + if { btrfs subvolume snapshot -- shared snapshot } > >>>>>> + > >>>>>> + # Validate the update directory. Delete any stale temporary files. > >>>>>> + # Check that a signature file was downloaded. > >>>>>> + if { updates-dir-check check snapshot } > >>>>>> + > >>>>>> + unshare --mount > >>>>>> + if { mount --bind -o ro -- snapshot /run/updater } > >>>>>> + > >>>>>> + /usr/lib/systemd/systemd-sysupdate update > >>>>> > >>>>> Why not just make a readonly snapshot? > >>>>> (btrfs subvolume snapshot -r) > >>>> > >>>> The checker will delete any temporary files it comes across, so it > >>>> needs write access. A snapshot is much heavier than a bind mount > >>>> and isn't automatically cleaned up. > >>> > >>> Okay, but why do we need to block systemd-sysupdate from writing to this > >>> directory, but not to anywhere else on the system? > >> > >> We don't. I'm fine with a writable mount. Either should work. > > > > Then let's keep things simple and drop the unshare and mount. We can > > deprivilege it properly in the future. > > The mount is absolutely necessary: it ensures that the update is > available where the .transfer file says it will be. It just doesn't > need to be read-only. > > The unshare is there to allow trivial cleanup by the kernel once > systemd-sysupdate exits. Ah, then I was misreading. If the mount has to be there, it might as well be read-only. With the outdated comment removed: Reviewed-by: Alyssa Ross