[Xenomai-core] [RFC][PATCH] security check for skin access

[Jan Kiszka <jan.kiszka@domain.hid>]

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Hi,

you all may know that Xenomai provides a bulk of very powerful
interfaces to userspace real-time applications. But not everyone may
have thought about the fact yet that these syscall extensions are
accessible for *all* users in the system!

Well, real-time and security is a more complex topic, but we should at
least restore the same level of security which Linux provides. For this
purpose, the attached (and long-planned) patch adds basic access control
to all Xenomai skin services by requiring CAP_SYS_NICE, i.e. the same
capability that is also required to manipulate the normal Linux
scheduling parameters.

I would suggest to merge it, either as an option (with default=y), or
unconditionally (it's just a tiny additional check in the syscall path).

Jan

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Index: ksrc/nucleus/shadow.c
===================================================================
--- ksrc/nucleus/shadow.c	(revision 719)
+++ ksrc/nucleus/shadow.c	(working copy)
@@ -1141,6 +1141,12 @@ static inline int do_hisyscall_event (un
     if (!__xn_reg_mux_p(regs))
 	goto linux_syscall;
 
+    if (unlikely(!cap_raised(p->cap_effective, CAP_SYS_NICE)))
+	{
+	__xn_error_return(regs,-EPERM);
+	return RTHAL_EVENT_STOP;
+	}
+
     muxid = __xn_mux_id(regs);
     muxop = __xn_mux_op(regs);
 

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