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Message-ID: <20080826185341.GA338@us.ibm.com>
Date: Tue, 26 Aug 2008 13:53:41 -0500
From: "Serge E. Hallyn" <serue@...ibm.com>
To: lkml <linux-kernel@...r.kernel.org>
Cc: "Eric W. Biederman" <ebiederm@...ssion.com>,
Andrew Morton <akpm@...l.org>
Subject: [PATCH 1/3] user namespaces: introduce user_struct->user_namespace
relationship
The following 3 patches are a small start to the long task of fleshing
out user namespace support. These three patches just clear up the
relationship of struct user_struct to struct user_namespace (patch 1),
fix up the refcounting (patch 2), and complete the action of switching
users when cloning a new user_namespace (patch 3).
Patch 1:
When a task does clone(CLONE_NEWNS), the task's user is the 'creator' of the
new user_namespace, and the user_namespace is tacked onto a list of those
created by this user.
Changelog:
Aug 25: make free_user not inlined as it's not trivial. (Eric
Biederman suggestion)
Aug 1: renamed user->user_namespace to user_ns, as the next
patch did anyway.
Aug 1: move put_user_ns call in one free_user() definition
to move it outside the lock in free_user. put_user_ns
calls free_user on the user_ns->creator, which in
turn would grab the lock again.
Signed-off-by: Serge Hallyn <serue@...ibm.com>
---
include/linux/sched.h | 1 +
include/linux/user_namespace.h | 1 +
kernel/user.c | 11 +++++++++--
kernel/user_namespace.c | 20 +++++++++++---------
4 files changed, 22 insertions(+), 11 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index cfb0d87..9bebf95 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -601,6 +601,7 @@ struct user_struct {
/* Hash table maintenance information */
struct hlist_node uidhash_node;
uid_t uid;
+ struct user_namespace *user_ns;
#ifdef CONFIG_USER_SCHED
struct task_group *tg;
diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index b5f41d4..f9477c3 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -13,6 +13,7 @@ struct user_namespace {
struct kref kref;
struct hlist_head uidhash_table[UIDHASH_SZ];
struct user_struct *root_user;
+ struct user_struct *creator;
};
extern struct user_namespace init_user_ns;
diff --git a/kernel/user.c b/kernel/user.c
index 865ecf5..ee841c7 100644
--- a/kernel/user.c
+++ b/kernel/user.c
@@ -22,6 +22,7 @@ struct user_namespace init_user_ns = {
.refcount = ATOMIC_INIT(2),
},
.root_user = &root_user,
+ .creator = &root_user,
};
EXPORT_SYMBOL_GPL(init_user_ns);
@@ -53,6 +54,7 @@ struct user_struct root_user = {
.files = ATOMIC_INIT(0),
.sigpending = ATOMIC_INIT(0),
.locked_shm = 0,
+ .user_ns = &init_user_ns,
#ifdef CONFIG_USER_SCHED
.tg = &init_task_group,
#endif
@@ -319,12 +321,13 @@ done:
* IRQ state (as stored in flags) is restored and uidhash_lock released
* upon function exit.
*/
-static inline void free_user(struct user_struct *up, unsigned long flags)
+static void free_user(struct user_struct *up, unsigned long flags)
{
/* restore back the count */
atomic_inc(&up->__count);
spin_unlock_irqrestore(&uidhash_lock, flags);
+ put_user_ns(up->user_ns);
INIT_WORK(&up->work, remove_user_sysfs_dir);
schedule_work(&up->work);
}
@@ -340,13 +343,14 @@ static inline void uids_mutex_unlock(void) { }
* IRQ state (as stored in flags) is restored and uidhash_lock released
* upon function exit.
*/
-static inline void free_user(struct user_struct *up, unsigned long flags)
+static void free_user(struct user_struct *up, unsigned long flags)
{
uid_hash_remove(up);
spin_unlock_irqrestore(&uidhash_lock, flags);
sched_destroy_user(up);
key_put(up->uid_keyring);
key_put(up->session_keyring);
+ put_user_ns(up->user_ns);
kmem_cache_free(uid_cachep, up);
}
@@ -409,6 +413,8 @@ struct user_struct *alloc_uid(struct user_namespace *ns, uid_t uid)
if (sched_create_user(new) < 0)
goto out_free_user;
+ new->user_ns = get_user_ns(ns);
+
if (uids_user_create(new))
goto out_destoy_sched;
@@ -441,6 +447,7 @@ struct user_struct *alloc_uid(struct user_namespace *ns, uid_t uid)
out_destoy_sched:
sched_destroy_user(new);
+ put_user_ns(new->user_ns);
out_free_user:
kmem_cache_free(uid_cachep, new);
out_unlock:
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 532858f..f9f7ad7 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -18,7 +18,6 @@
static struct user_namespace *clone_user_ns(struct user_namespace *old_ns)
{
struct user_namespace *ns;
- struct user_struct *new_user;
int n;
ns = kmalloc(sizeof(struct user_namespace), GFP_KERNEL);
@@ -37,15 +36,17 @@ static struct user_namespace *clone_user_ns(struct user_namespace *old_ns)
return ERR_PTR(-ENOMEM);
}
- /* Reset current->user with a new one */
- new_user = alloc_uid(ns, current->uid);
- if (!new_user) {
- free_uid(ns->root_user);
- kfree(ns);
- return ERR_PTR(-ENOMEM);
- }
+ /* pin the creating user */
+ ns->creator = current->user;
+ atomic_inc(&ns->creator->__count);
+
+ /*
+ * The alloc_uid() incremented the userns refcount,
+ * so drop it again
+ */
+ put_user_ns(ns);
- switch_uid(new_user);
+ switch_uid(ns->root_user);
return ns;
}
@@ -71,6 +72,7 @@ void free_user_ns(struct kref *kref)
ns = container_of(kref, struct user_namespace, kref);
release_uids(ns);
+ free_uid(ns->creator);
kfree(ns);
}
EXPORT_SYMBOL(free_user_ns);
--
1.5.4.3
--
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