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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>
zero-sugar-mainline-defconfig
Kirill Tkhai 2020-08-03 13:16:37 +03:00 committed by Christian Brauner
parent 8eb71d95f3
commit 265cbd62e0
No known key found for this signature in database
GPG Key ID: 91C61BC06578DCA2
3 changed files with 5 additions and 6 deletions
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5
include/linux/user_namespace.h
View File

@ -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);
}

2
kernel/user.c
View File

@ -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,

4
kernel/user_namespace.c
View File

@ -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)