Date: Mon, 20 Jun 2011 20:43:57 +1000 (EST) From: James Morris <jmorris@...ei.org> To: Vasiliy Kulikov <segoon@...nwall.com> cc: kernel-hardening@...ts.openwall.com, linux-kernel@...r.kernel.org, linux-security-module@...r.kernel.org Subject: Re: [RFC 2/5 v4] procfs: add hidepid= and gid= mount options On Mon, 20 Jun 2011, Vasiliy Kulikov wrote: > > Can you provide evidence that this is a useful feature? e.g. examples of > > exploits / techniques which would be _usefully_ hampered or blocked. > > First, most of these files are usefull in sense of statistics gathering > and debugging. There is no reason to provide this information to the > world. > > Second, yes, it blocks one source of information used in timing attacks, > just use reading the counters as more or less precise time measurement > when actual timing measurements are not precise enough. Can you provide concrete examples? > > > hidepid=1 means users may not access any /proc/<pid>/ directories, but their > > > own. Sensitive files like cmdline, io, sched*, status, wchan are now > > > protected against other users. As permission checking done in > > > proc_pid_permission() and files' permissions are left untouched, > > > programs expecting specific files' permissions are not confused. > > > > IMHO such programs are beyond broken and have voided their kernel > > warranty. > > Policykit, Debian's start-stop-daemon, util-linux use /proc/PID's uid. > procps use both /proc/PID's uid and gid. Are all of them totally broken? If they depend on specific permissions, yes. To access the information, why not just create a group with Unix read access to these files? - James -- James Morris <jmorris@...ei.org>
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