Messages in this thread Patch in this message | | | Date | Wed, 11 Feb 2009 13:38:46 -0600 | From | "Serge E. Hallyn" <> | Subject | Re: namespaces?: bug at mm/slub.c:2750 |
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Quoting David Howells (dhowells@redhat.com): > Serge E. Hallyn <serue@us.ibm.com> wrote: > > > It's called under uidhash_lock spinlock so should be ok, but in > > principle you're right so it's probably a good idea. > > The lock is nothing to do with it. put_user_ns() may call kfree() on the > user_namespace, but the user_struct given to uid_hash_remove() may still be > attached to it.
Yes, but noone will pull the user_struct off the list without taking the lock.
what am I missing?
Anyway, I do like swapping the lines (as below) better.
-serge
From 8b83d11023c1064e99bffae3c2a05580b915de60 Mon Sep 17 00:00:00 2001 From: Serge E. Hallyn <serue@us.ibm.com> Date: Wed, 11 Feb 2009 11:29:52 -0500 Subject: [PATCH 1/1] user namespaces: only put the userns when we unhash the uid
uids in namespaces other than init don't get a sysfs entry.
For those in the init namespace, while we're waiting to remove the sysfs entry for the uid the uid is still hashed, and alloc_uid() may re-grab that uid without getting a new reference to the user_ns, which we've already put in free_user before scheduling remove_user_sysfs_dir().
Signed-off-by: Serge E. Hallyn <serue@us.ibm.com> --- kernel/user.c | 3 +-- 1 files changed, 1 insertions(+), 2 deletions(-)
diff --git a/kernel/user.c b/kernel/user.c index 477b666..3551ac7 100644 --- a/kernel/user.c +++ b/kernel/user.c @@ -72,6 +72,7 @@ static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent) static void uid_hash_remove(struct user_struct *up) { hlist_del_init(&up->uidhash_node); + put_user_ns(up->user_ns); } static struct user_struct *uid_hash_find(uid_t uid, struct hlist_head *hashent) @@ -334,7 +335,6 @@ static void free_user(struct user_struct *up, unsigned long flags) 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); } @@ -357,7 +357,6 @@ static void free_user(struct user_struct *up, unsigned long 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); } -- 1.6.1
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