user: Use generic ns_common::count

Switch over user 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/159644979754.604812.601625186726406922.stgit@localhost.localdomain
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index 6ef1c7109fc4d42bf2f408a01cdef9cafadaf471..64cf8ebdc4ec9434af97ea8a68ff801021378fed 100644 (file)
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -57,7 +57,6 @@ struct user_namespace {
        struct uid_gid_map      uid_map;
        struct uid_gid_map      gid_map;
        struct uid_gid_map      projid_map;
-       atomic_t                count;
        struct user_namespace   *parent;
        int                     level;
        kuid_t                  owner;
@@ -109,7 +108,7 @@ void dec_ucount(struct ucounts *ucounts, enum ucount_type type);
 static inline struct user_namespace *get_user_ns(struct user_namespace *ns)
 {
        if (ns)
-               atomic_inc(&ns->count);
+               refcount_inc(&ns->ns.count);
        return ns;
 }
 
@@ -119,7 +118,7 @@ extern void __put_user_ns(struct user_namespace *ns);
 
 static inline void put_user_ns(struct user_namespace *ns)
 {
-       if (ns && atomic_dec_and_test(&ns->count))
+       if (ns && refcount_dec_and_test(&ns->ns.count))
                __put_user_ns(ns);
 }
 

diff --git a/kernel/user.c b/kernel/user.c
index b1635d94a1f246185c740cd268303beb609de8bf..a2478cddf536e440664a53d1e0f730c29c68f581 100644 (file)
--- a/kernel/user.c
+++ b/kernel/user.c
@@ -55,7 +55,7 @@ struct user_namespace init_user_ns = {
                        },
                },
        },
-       .count = ATOMIC_INIT(3),
+       .ns.count = REFCOUNT_INIT(3),
        .owner = GLOBAL_ROOT_UID,
        .group = GLOBAL_ROOT_GID,
        .ns.inum = PROC_USER_INIT_INO,

diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 87804e0371fe19b91a9e6e7d5092cd9814104531..7c2bbe8f3e450818b3fb2ae36e61193bcb39ac9c 100644 (file)
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -111,7 +111,7 @@ int create_user_ns(struct cred *new)
                goto fail_free;
        ns->ns.ops = &userns_operations;
 
-       atomic_set(&ns->count, 1);
+       refcount_set(&ns->ns.count, 1);
        /* Leave the new->user_ns reference with the new user namespace. */
        ns->parent = parent_ns;
        ns->level = parent_ns->level + 1;
@@ -197,7 +197,7 @@ static void free_user_ns(struct work_struct *work)
                kmem_cache_free(user_ns_cachep, ns);
                dec_user_namespaces(ucounts);
                ns = parent;
-       } while (atomic_dec_and_test(&parent->count));
+       } while (refcount_dec_and_test(&parent->ns.count));
 }
 
 void __put_user_ns(struct user_namespace *ns)