uts: Use generic ns_common::count

Switch over uts 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/159644978167.604812.1773586504374412107.stgit@localhost.localdomain
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

diff --git a/include/linux/utsname.h b/include/linux/utsname.h
index 44429d9142ca3d08309435d7fe27e4ade7038103..2b1737c9b244dd77047b82de3ebda83d6a6310f0 100644 (file)
--- a/include/linux/utsname.h
+++ b/include/linux/utsname.h
@@ -4,7 +4,6 @@
 
 
 #include <linux/sched.h>
-#include <linux/kref.h>
 #include <linux/nsproxy.h>
 #include <linux/ns_common.h>
 #include <linux/err.h>
@@ -22,7 +21,6 @@ struct user_namespace;
 extern struct user_namespace init_user_ns;
 
 struct uts_namespace {
-       struct kref kref;
        struct new_utsname name;
        struct user_namespace *user_ns;
        struct ucounts *ucounts;
@@ -33,16 +31,17 @@ extern struct uts_namespace init_uts_ns;
 #ifdef CONFIG_UTS_NS
 static inline void get_uts_ns(struct uts_namespace *ns)
 {
-       kref_get(&ns->kref);
+       refcount_inc(&ns->ns.count);
 }
 
 extern struct uts_namespace *copy_utsname(unsigned long flags,
        struct user_namespace *user_ns, struct uts_namespace *old_ns);
-extern void free_uts_ns(struct kref *kref);
+extern void free_uts_ns(struct uts_namespace *ns);
 
 static inline void put_uts_ns(struct uts_namespace *ns)
 {
-       kref_put(&ns->kref, free_uts_ns);
+       if (refcount_dec_and_test(&ns->ns.count))
+               free_uts_ns(ns);
 }
 
 void uts_ns_init(void);

diff --git a/init/version.c b/init/version.c
index cba341161b5801967ae97ade76b6c9a5522961ac..80d2b7566b397d8698f86a5dbf8669b5f0abb10e 100644 (file)
--- a/init/version.c
+++ b/init/version.c
@@ -25,7 +25,7 @@ int version_string(LINUX_VERSION_CODE);
 #endif
 
 struct uts_namespace init_uts_ns = {
-       .kref = KREF_INIT(2),
+       .ns.count = REFCOUNT_INIT(2),
        .name = {
                .sysname        = UTS_SYSNAME,
                .nodename       = UTS_NODENAME,

diff --git a/kernel/utsname.c b/kernel/utsname.c
index e488d0e2ab457b5f24c3c9c999cc49c7870b6839..b1ac3ca870f24e94dd867bc0cc5fc1541e7b9645 100644 (file)
--- a/kernel/utsname.c
+++ b/kernel/utsname.c
@@ -33,7 +33,7 @@ static struct uts_namespace *create_uts_ns(void)
 
        uts_ns = kmem_cache_alloc(uts_ns_cache, GFP_KERNEL);
        if (uts_ns)
-               kref_init(&uts_ns->kref);
+               refcount_set(&uts_ns->ns.count, 1);
        return uts_ns;
 }
 
@@ -103,11 +103,8 @@ struct uts_namespace *copy_utsname(unsigned long flags,
        return new_ns;
 }
 
-void free_uts_ns(struct kref *kref)
+void free_uts_ns(struct uts_namespace *ns)
 {
-       struct uts_namespace *ns;
-
-       ns = container_of(kref, struct uts_namespace, kref);
        dec_uts_namespaces(ns->ucounts);
        put_user_ns(ns->user_ns);
        ns_free_inum(&ns->ns);