linux-kernel - [PATCH] User namespaces: Only put the userns when we unhash the uid

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Date:	Fri, 13 Feb 2009 14:04:21 +0000
From:	David Howells <dhowells@...hat.com>
To:	torvalds@...l.org, jmorris@...ei.sys
Cc:	akpm@...ux-foundation.org, dhowells@...hat.com, serue@...ibm.com,
	mingo@...e.hu, kosaki.motohiro@...fujitsu.com,
	linux-kernel@...r.kernel.org, vegard.nossum@...il.com,
	containers@...ts.osdl.org, snakebyte@....de
Subject: [PATCH] User namespaces: Only put the userns when we unhash the uid

From: Serge E. Hallyn <serue@...ibm.com>

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().

Reported-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Signed-off-by: Serge E. Hallyn <serue@...ibm.com>
Acked-by: David Howells <dhowells@...hat.com>
Tested-by: Ingo Molnar <mingo@...e.hu>
---

 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);
 }
 

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