On Wed, 2018-02-14 at 09:42 -0600, Serge E. Hallyn wrote: > Quoting Mimi Zohar (zohar@xxxxxxxxxxxxxxxxxx): > > 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. > > I don't think I'm being clear. > > In your patch it looks like you mark unprivileged FUSE mounts as > INTEGRITY_FAIL. I agree you should do that. But you skip the > FS_UNTRUSTED check for privileged FUSE mounts. I'm asking why > that's ok. > > > > > 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"? > > My point was - I was asking whether there was any way to have IMA be > meaningful with such containers, not saying I had any ideas, and > certainly not saying that just because you can't detect it means you > should allow it in all cases. It's too bad that it has this effect, > but I agree with your patch. > > I only didn't ack it because you're skipping the check for privileged > mounts which seems wrong. Oh! That is based on Linus' "request" not to break userspace. Mimi
