Re: [PATCH] Allow restricting permissions in /proc/sys

On Wed, Nov 13, 2019 at 5:19 PM Topi Miettinen [off-list ref] wrote:

On 13.11.2019 18.00, Jann Horn wrote:

quoted

On Wed, Nov 13, 2019 at 12:22 AM Christian Brauner
[off-list ref] wrote:

quoted

On Sun, Nov 03, 2019 at 04:55:48PM +0200, Topi Miettinen wrote:

quoted

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.

[...]

quoted

In kernel/ucount.c, the ->permissions handler set_permissions() grants
access based on whether the caller has CAP_SYS_RESOURCE. And in
net/sysctl_net.c, the handler net_ctl_permissions() grants access
based on whether the caller has CAP_NET_ADMIN. This added check is
going to break those, right?

Right. The comment above seems then a bit misleading:
        /*
         * sysctl entries that are not writeable,
         * are _NOT_ writeable, capabilities or not.
         */

I don't see the problem. Those handlers never make a file writable
that doesn't have one of the three write bits (0222) set.