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Commit 304362a8 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 

Pull namespace fix from Eric Biederman:
 "This fixes a race between put_ucounts and get_ucounts that can cause a
  use after free. The fix works by simplifying the code and so there is
  not even a temptation to be clever and play spinlock vs atomic
  reference games"

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace:
  ucount: Remove the atomicity from ucount->count
parents f26db964 040757f7

include/linux/user_namespace.h

+1 −1
Original line number Diff line number Diff line
@@ -72,7 +72,7 @@ struct ucounts { 
	struct hlist_node node;

	struct user_namespace *ns;

	kuid_t uid;

	atomic_t count;

	int count;

	atomic_t ucount[UCOUNT_COUNTS];

};

kernel/ucount.c

+11 −7
Original line number Diff line number Diff line
@@ -144,7 +144,7 @@ static struct ucounts *get_ucounts(struct user_namespace *ns, kuid_t uid) 


		new->ns = ns;

		new->uid = uid;

		atomic_set(&new->count, 0);

		new->count = 0;



		spin_lock_irq(&ucounts_lock);

		ucounts = find_ucounts(ns, uid, hashent);
@@ -155,8 +155,10 @@ static struct ucounts *get_ucounts(struct user_namespace *ns, kuid_t uid) 
			ucounts = new;

		}

	}

	if (!atomic_add_unless(&ucounts->count, 1, INT_MAX))

	if (ucounts->count == INT_MAX)

		ucounts = NULL;

	else

		ucounts->count += 1;

	spin_unlock_irq(&ucounts_lock);

	return ucounts;

}
@@ -165,14 +167,16 @@ static void put_ucounts(struct ucounts *ucounts) 
{

	unsigned long flags;



	if (atomic_dec_and_test(&ucounts->count)) {

	spin_lock_irqsave(&ucounts_lock, flags);

	ucounts->count -= 1;

	if (!ucounts->count)

		hlist_del_init(&ucounts->node);

	else

		ucounts = NULL;

	spin_unlock_irqrestore(&ucounts_lock, flags);



	kfree(ucounts);

}

}



static inline bool atomic_inc_below(atomic_t *v, int u)

{