Topi Miettinen <toiwoton@xxxxxxxxx> writes: > On 3.11.2019 20.50, Eric W. Biederman wrote: >> Topi Miettinen <toiwoton@xxxxxxxxx> writes: >> >>> Several items in /proc/sys need not be accessible to unprivileged >>> tasks. Let the system administrator change the permissions, but only >>> to more restrictive modes than what the sysctl tables allow. >> >> This looks quite buggy. You neither update table->mode nor >> do you ever read from table->mode to initialize the inode. >> I am missing something in my quick reading of your patch? > > inode->i_mode gets initialized in proc_sys_make_inode(). > > I didn't want to touch the table, so that the original permissions can > be used to restrict the changes made. In case the restrictions are > removed as suggested by Theodore Ts'o, table->mode could be > changed. Otherwise I'd rather add a new field to store the current > mode and the mode field can remain for reference. As the original > author of the code from 2007, would you let the administrator to > chmod/chown the items in /proc/sys without restrictions (e.g. 0400 -> > 0777)? At an architectural level I think we need to do this carefully and have a compelling reason. The code has survived nearly the entire life of linux without this capability. I think right now the common solution is to mount another file over the file you are trying to hide/limit. Changing the permissions might be better but that is not at all clear. Do you have specific examples of the cases where you would like to change the permissions? >> The not updating table->mode almost certainly means that as soon as the >> cached inode is invalidated the mode changes will disappear. Not to >> mention they will fail to propogate between different instances of >> proc. >> >> Loosing all of your changes at cache invalidation seems to make this a >> useless feature. > > At least different proc instances seem to work just fine here (they > show the same changes), but I suppose you are right about cache > invalidation. It is going to take the creation of a pid namespace to see different proc instances. All mounts of the proc within the same pid_namespace return the same instance. Eric
