Hello, Eric. On Tue, Nov 06, 2012 at 08:10:10AM -0800, Eric W. Biederman wrote: > mknod is gated by the vfs with a capability call. > > open does not perform the CAP_MKNOD check. > > Since the device cgroup prevents opening of device nodes adding > permission to access a new device node (update_access) is roughly > equivalent to mknod when the device cgroup does not exist. I think that's a jump. > To preserve the notion that only a privileged user can grant access to > device nodes we need a capability check. Especially since the device > cgroup is designed to limit processes with uid == 0. > > Without a capability check a process with CAP_DAC_OVERRIDE can go > shopping for a device control group that happens to have the device it > wants to use. > > Similary without a capability check a process with CAP_DAD_OVERRIDE can > add or remove any device node into a device control group. > > I don't see how the device control group can limit uid == 0 with the > device control group without making the operations require a capability > you don't give to ever user who has uid == 0. devices cgroup adds to restrictions what a group of tasks can do. Access to cgroup configuration is gated by cgroup core (currently by VFS permissions) and that's it. I really don't want each controller to develop its own permission checks. If a controller can't live with that, it probably shouldn't be a cgroup controller. So, if you think the CAP check is needed for cgroup in general (and can justify it), please feel free to move it to cgroup core; otherwise, the CAP check is going away from devices and if devices can't live with that, it probably shouldn't have been a cgroup controller from the beginning. Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
