Date: Tue, 30 May 2017 10:52:35 -0500 From: "Serge E. Hallyn" <serge@...lyn.com> To: Peter Dolding <oiaohm@...il.com> Cc: "Serge E. Hallyn" <serge@...lyn.com>, Kees Cook <keescook@...omium.org>, Daniel Micay <danielmicay@...il.com>, Alan Cox <gnomes@...rguk.ukuu.org.uk>, Matt Brown <matt@...tt.com>, Greg KH <gregkh@...uxfoundation.org>, Jiri Slaby <jslaby@...e.com>, Andrew Morton <akpm@...ux-foundation.org>, Jann Horn <jannh@...gle.com>, James Morris <jmorris@...ei.org>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, linux-security-module <linux-security-module@...r.kernel.org>, linux-kernel <linux-kernel@...r.kernel.org> Subject: Re: Re: [PATCH v6 0/2] security: tty: make TIOCSTI ioctl require CAP_SYS_ADMIN Quoting Peter Dolding (oiaohm@...il.com): > On Sat, May 20, 2017 at 12:33 AM, Serge E. Hallyn <serge@...lyn.com> wrote: > > On Fri, May 19, 2017 at 12:48:17PM +1000, Peter Dolding wrote: > >> Using cap_sys_admin as fix is like removing car windsheld because > >> vision is being blocked by a rock hitting it. > > > > Nonsense. If the application has cap_sys_admin then it is less contained and > > more trusted anyway. If I went to the trouble to run an application in a > > private user namespace (where it can have cap_sys_admin, but not targeted > > at my tty) then it should be more contained. That's the point of targeted > > capabilities. > > The thing that is missed every time is how much is cap_sys_admin. > > So you are saying a user namespace has to be set up to contain the defect. > > Really no application should have cap_sys_admin. > > The theory of capabilities is that security should be broken down into > logical blocks. > > So tty stuff should under a tty capabilities. (last reply on this) Currently capabilities.7 says * employ the TIOCSTI ioctl(2) to insert characters into the input queue of a terminal other than the caller's controlling terminal; for CAP_SYS_ADMIN. So you can create a new CAP_SYS_TIOCSSTI if you like, and offer a patch where *both* CAP_SYS_ADMIN and CAP_SYS_ADMIN suffice. Again, see CAP_SYSLOG for a prior example. What you may not do is change it so that on an older kernel you must have CAP_SYS_ADMIN to use TIOCSTI, while on a newer one it does not suffice. -serge
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