On Wed, 2018-02-14 at 09:16 -0600, Serge E. Hallyn wrote: > Quoting Mimi Zohar (zohar@xxxxxxxxxxxxxxxxxx): > > On Wed, 2018-02-14 at 08:49 -0600, Serge E. Hallyn wrote: > > > Quoting Mimi Zohar (zohar@xxxxxxxxxxxxxxxxxx): > > > > Files on untrusted filesystems, such as fuse, can change at any time, > > > > making the measurement(s) and by extension signature verification > > > > meaningless. > > > > > > > > FUSE can be mounted by unprivileged users either today with fusermount > > > > installed with setuid, or soon with the upcoming patches to allow FUSE > > > > mounts in a non-init user namespace. > > > > > > > > This patch always fails the file signature verification on unprivileged > > > > and untrusted filesystems. To also fail file signature verification on > > > > > > Why only untrusted? Fuse could cause the same issue if it just > > > messes up when mounted from init userns right? > > > > Right, whether it is an unprivileged mount or not, fuse can return > > whatever it wants, whenever it wants. IMA can calculate the file hash > > based based on what it reads, but fuse can return whatever it wants on > > subsequent reads. > > Ok but your patch seems to let privileged fuse mounts slide? (see below) Unprivileged fuse mounts hasn't been upstreamed yet, so we wouldn't be breaking existing userspace. > > > Refer to the discussion with Linus - http://kernsec.org/pipermail/linu > > x-security-module-archive/2018-February/005200.html > > > > > > privileged, untrusted filesystems requires a custom policy. > > > > > > (I'm not saying you shouldn't do this, but) does this mean that > > > a container whose rootfs is fuse-mounted by the unprivileged user > > > cannot possibly use IMA? > > > > How would you suggest to differentiate between your unprivileged fuse > > mounts from unintended, unintended malicious ones? > > I wouldn't. What happened to the requirement that systems should be "fail-safe"? Ok, hard coding this rule probably is not a good idea. For those wanting to take this liability on their systems, we can make this configurable, like for privileged fuse mounts. Unlike for privileged fuse mounts, the builtin policies, I think, should be fail safe and include the "fail" rule for unprivileged fuse mounts. > > > The remaining patches are policy based. > > > > > Good thing we can partially work around that by intercepting real > > > mount calls with Tycho's new patchset :) > > > > Can you provide a little more details? > > It would allow a container runtime to intercept mount(2) and perform > a real mount on the user's behalf. Assuming the runtime is privileged, > of course, otherwise it would intercept and do a fuse mount which is > no help here :) > > https://lkml.org/lkml/2018/2/4/28 thanks! Mimi
