From: Neil Horman <nhorman@redhat.com>
Date: Thu, 2 Oct 2008 16:16:10 -0400
Subject: [net] correct mode setting for extended sysctl interface
Message-id: 20081002201610.GD14508@hmsendeavour.rdu.redhat.com
O-Subject: [RHEL 5.3 patch] correct mode settings for extended sysctls on net interfaces (bz 463659)
Bugzilla: 463659
RH-Acked-by: Don Howard <dhoward@redhat.com>
RH-Acked-by: Andy Gospodarek <gospo@redhat.com>
RH-Acked-by: Thomas Graf <tgraf@redhat.com>

Hey all-
	A few weeks back I posted a patch that implemented the ability to add
net devconf sysctls to dynamically allocated network interfaces without breaking
ABI.  As part of this patch I needed to handle the semantics of those added
sysctls for interfaces that were not dynamically allocated (and consequently did
not have the additional storage for extended sysctls).  I solved this by marking
the associated proc files as having no permissions (so they could not be read or
written).  Well, unfortunately, sysctl registration automatically marks sysctl
files as being readable, regardless of the mode that you set, so we just
discovered this oddness that on interfaces like l0, which are not dynamically
allocated, extended sysctls are shows as readable, but trying to read them,
still returns -EPERM.  I'm solving this problem by attaching the default storage
data for the extended sysctls to statically allocated net_devices and marking
them as read only.  This way reading for instance
/proc/sys/net/ipv6/conf/lo/accept_dad returns the default value of that sysctl,
but it still remains unwriteable.

Tested by me.  Solves bz 463659

Regards
Neil

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 3744762..1f89683 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -4056,7 +4056,7 @@ static void addrconf_sysctl_register(struct inet6_dev *idev, struct ipv6_devconf
 					 * register the extra sysctls, but we give them
 					 * no permissions so that we can't write to them
 					 */
-					t->addrconf_vars[i].mode = 0000;
+					t->addrconf_vars[i].mode = 0444;
 			} else
 				dext = &ext->ipv6_devconf_ext;