Miklos Szeredi <miklos@xxxxxxxxxx> writes: >> > That depends. Current patches check the "unprivileged submounts >> > allowed under this mount" flag only on the requested mount and not on >> > the propagated mounts. Do you see a problem with this? >> >> I think privileges of this sort should propagate. If I read what you >> just said correctly if I have a private mount namespace I won't be able >> to mount anything unless when it was setup the unprivileged submount >> command was explicitly set. > > By design yes. Why is that a problem? It certainly doesn't match my intuition. Why are directory permissions not sufficient to allow/deny non-priveleged mounts? I don't understand that contention yet. I should probably go back and look and see how plan9 handles mount/unmount permissions. Plan9 gets away with a lot more because it doesn't have a suid bit and mount namespaces were always present, so they don't have backwards compatibility problems. My best guess at the moment is that plan9 treated mount/unmount as completely unprivileged and used the mount namespaces to limit the scope of what would be affected by a mount/unmount operation. I think that may be reasonable in linux as well but it will require the presence of a mount namespace to limit the affects of what a user can do. So short of a more thorough audit I believe the final semantics should be: - mount/unmount for non-priveleged processes should only be limited by the mount namespace and directory permissions. - CLONE_NEWNS should not be a privileged operation. What prevents us from allowing these things? - Unprivileged CLONE_NEWNS and unprivileged mounts needs resource accounting so we don't have a denial of service attack. - Unprivileged mounts must be limited to directories that we have permission to modify in a way that we could get the same effect as the mount or unmount operation in terms of what files are visible otherwise we can mess up SUID executables. - Anything else? There are user space issues such as a reasonable pam module and how to do backups. However those are user space issues. What am I missing that requires us to add MNT_USER and MNT_USERMNT? Eric - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
