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SubjectRe: [CFT][PATCH 6/7] userns: Add a knob to disable setgroups on a per user namespace basis
On Mon, Dec 8, 2014 at 2:11 PM, Eric W. Biederman <ebiederm@xmission.com> wrote:
>
> - Expose the knob to user space through a proc file /proc/<pid>/setgroups
>
> A value of 0 means the setgroups system call is disabled in the

"deny"

> current processes user namespace and can not be enabled in the
> future in this user namespace.
>
> A value of 1 means the segtoups system call is enabled.
>

"allow"

> - Descedent user namespaces inherit the value of setgroups from

s/Descedent/Descendent/

> --- a/kernel/groups.c
> +++ b/kernel/groups.c
> @@ -222,6 +222,7 @@ bool may_setgroups(void)
> * the user namespace has been established.
> */
> return userns_gid_mappings_established(user_ns) &&
> + userns_setgroups_allowed(user_ns) &&
> ns_capable(user_ns, CAP_SETGID);
> }

Can you add a comment explaining the ordering? For example:

We need to check for a gid mapping before checking setgroups_allowed
because an unprivileged user can create a userns with setgroups
allowed, then disallow setgroups and add a mapping. If we check in
the opposite order, then we have a race: we could see that setgroups
is allowed before the user clears the bit and then see that there is a
gid mapping after the other thread is done.

--Andy


--
Andy Lutomirski
AMA Capital Management, LLC


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