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

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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
This commit is contained in:
Linus Torvalds 2017-03-07 10:06:25 -08:00
commit 304362a8bc
2 changed files with 12 additions and 8 deletions
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2
include/linux/user_namespace.h
View file

@ -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];
};

18
kernel/ucount.c
View file

@ -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;
}
@ -165,13 +167,15 @@ static void put_ucounts(struct ucounts *ucounts)
{
unsigned long flags;
if (atomic_dec_and_test(&ucounts->count)) {
spin_lock_irqsave(&ucounts_lock, flags);
spin_lock_irqsave(&ucounts_lock, flags);
ucounts->count -= 1;
if (!ucounts->count)
hlist_del_init(&ucounts->node);
spin_unlock_irqrestore(&ucounts_lock, flags);
else
ucounts = NULL;
spin_unlock_irqrestore(&ucounts_lock, flags);
kfree(ucounts);
}
kfree(ucounts);
}
static inline bool atomic_inc_below(atomic_t *v, int u)