cgroup: Use generic ns_common::count

Switch over cgroup namespaces to use the newly introduced common lifetime
counter.

Currently every namespace type has its own lifetime counter which is stored
in the specific namespace struct. The lifetime counters are used
identically for all namespaces types. Namespaces may of course have
additional unrelated counters and these are not altered.

This introduces a common lifetime counter into struct ns_common. The
ns_common struct encompasses information that all namespaces share. That
should include the lifetime counter since its common for all of them.

It also allows us to unify the type of the counters across all namespaces.
Most of them use refcount_t but one uses atomic_t and at least one uses
kref. Especially the last one doesn't make much sense since it's just a
wrapper around refcount_t since 2016 and actually complicates cleanup
operations by having to use container_of() to cast the correct namespace
struct out of struct ns_common.

Having the lifetime counter for the namespaces in one place reduces
maintenance cost. Not just because after switching all namespaces over we
will have removed more code than we added but also because the logic is
more easily understandable and we indicate to the user that the basic
lifetime requirements for all namespaces are currently identical.

Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Link: https://lore.kernel.org/r/159644980994.604812.383801057081594972.stgit@localhost.localdomain
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 618838c48313cd82a9ce917378a5508396b0dcee..451c2d26a5db8425394fce3ab27736ce61eb58c7 100644 (file)
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -854,7 +854,6 @@ static inline void cgroup_sk_free(struct sock_cgroup_data *skcd) {}
 #endif /* CONFIG_CGROUP_DATA */
 
 struct cgroup_namespace {
-       refcount_t              count;
        struct ns_common        ns;
        struct user_namespace   *user_ns;
        struct ucounts          *ucounts;
@@ -889,12 +888,12 @@ copy_cgroup_ns(unsigned long flags, struct user_namespace *user_ns,
 static inline void get_cgroup_ns(struct cgroup_namespace *ns)
 {
        if (ns)
-               refcount_inc(&ns->count);
+               refcount_inc(&ns->ns.count);
 }
 
 static inline void put_cgroup_ns(struct cgroup_namespace *ns)
 {
-       if (ns && refcount_dec_and_test(&ns->count))
+       if (ns && refcount_dec_and_test(&ns->ns.count))
                free_cgroup_ns(ns);
 }
 

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index dd247747ec14a622d47037e66e5b43dfbd4e6f24..22e4669268534b7cc22f0524a91cd835a221494a 100644 (file)
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -199,7 +199,7 @@ static u16 have_canfork_callback __read_mostly;
 
 /* cgroup namespace for init task */
 struct cgroup_namespace init_cgroup_ns = {
-       .count          = REFCOUNT_INIT(2),
+       .ns.count       = REFCOUNT_INIT(2),
        .user_ns        = &init_user_ns,
        .ns.ops         = &cgroupns_operations,
        .ns.inum        = PROC_CGROUP_INIT_INO,

diff --git a/kernel/cgroup/namespace.c b/kernel/cgroup/namespace.c
index 812a61afd538a180d64b3ec35dbf3d978c7a059a..f5e8828c109cf8b5ab866d823d5dd6a1e58b4800 100644 (file)
--- a/kernel/cgroup/namespace.c
+++ b/kernel/cgroup/namespace.c
@@ -32,7 +32,7 @@ static struct cgroup_namespace *alloc_cgroup_ns(void)
                kfree(new_ns);
                return ERR_PTR(ret);
        }
-       refcount_set(&new_ns->count, 1);
+       refcount_set(&new_ns->ns.count, 1);
        new_ns->ns.ops = &cgroupns_operations;
        return new_ns;
 }