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| author | Linus Torvalds <torvalds@linux-foundation.org> | 2017-03-07 19:06:25 +0100 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2017-03-07 19:06:25 +0100 |
| commit | 304362a8bce1a5b7f9491be5a0643cd14a52364d (patch) | |
| tree | c1e54257a4e9cc5327cb4c84e566a8869af62b6e /kernel | |
| parent | Merge tag 'trace-v4.11-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/... (diff) | |
| parent | ucount: Remove the atomicity from ucount->count (diff) | |
| download | linux-304362a8bce1a5b7f9491be5a0643cd14a52364d.tar.xz linux-304362a8bce1a5b7f9491be5a0643cd14a52364d.zip | |
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
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/ucount.c | 18 |
1 files changed, 11 insertions, 7 deletions
diff --git a/kernel/ucount.c b/kernel/ucount.c index 62630a40ab3a..b4eeee03934f 100644 --- a/kernel/ucount.c +++ b/kernel/ucount.c @@ -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) |