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.

Kirill Tkhai committed 6 years ago

Commit 265cbd61 parent 8eb71d93 files · +5 −6Browse files

Unified · Split

3 files

include/linux/user_namespace.h +2 −3
kernel/user.c +1 −1
kernel/user_namespace.c +2 −2

include/linux/user_namespace.h+2−3

@@ -57,7 +57,6 @@ struct user_namespace { · 56 unmodified lines
57	57	struct uid_gid_map uid_map;
58	58	struct uid_gid_map gid_map;
59	59	struct uid_gid_map projid_map;
60		− atomic_t count;
61	60	struct user_namespace *parent;
62	61	int level;
63	62	kuid_t owner;
@@ -109,7 +108,7 @@ void dec_ucount(struct ucounts *ucounts, enum ucount_type type); · 45 unmodified lines
109	108	static inline struct user_namespace get_user_ns(struct user_namespace ns)
110	109	{
111	110	if (ns)
112		− atomic_inc(&ns->count);
	111	+ refcount_inc(&ns->ns.count);
113	112	return ns;
114	113	}
115	114
@@ -119,7 +118,7 @@ extern void __put_user_ns(struct user_namespace *ns); · 3 unmodified lines
119	118
120	119	static inline void put_user_ns(struct user_namespace *ns)
121	120	{
122		− if (ns && atomic_dec_and_test(&ns->count))
	121	+ if (ns && refcount_dec_and_test(&ns->ns.count))
123	122	__put_user_ns(ns);
124	123	}
125	124

kernel/user.c+1−1

@@ -55,7 +55,7 @@ struct user_namespace init_user_ns = { · 54 unmodified lines
55	55	},
56	56	},
57	57	},
58		− .count = ATOMIC_INIT(3),
	58	+ .ns.count = REFCOUNT_INIT(3),
59	59	.owner = GLOBAL_ROOT_UID,
60	60	.group = GLOBAL_ROOT_GID,
61	61	.ns.inum = PROC_USER_INIT_INO,

kernel/user_namespace.c+2−2

@@ -111,7 +111,7 @@ int create_user_ns(struct cred *new) · 110 unmodified lines
111	111	goto fail_free;
112	112	ns->ns.ops = &userns_operations;
113	113
114		− atomic_set(&ns->count, 1);
	114	+ refcount_set(&ns->ns.count, 1);
115	115	/* Leave the new->user_ns reference with the new user namespace. */
116	116	ns->parent = parent_ns;
117	117	ns->level = parent_ns->level + 1;
@@ -197,7 +197,7 @@ static void free_user_ns(struct work_struct *work) · 79 unmodified lines
197	197	kmem_cache_free(user_ns_cachep, ns);
198	198	dec_user_namespaces(ucounts);
199	199	ns = parent;
200		− } while (atomic_dec_and_test(&parent->count));
	200	+ } while (refcount_dec_and_test(&parent->ns.count));
201	201	}
202	202
203	203	void __put_user_ns(struct user_namespace *ns)

user: Use generic ns_common::count

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