The futex_requeue function in kernel/futex.c in the Linux kernel through 3.14.5 does not ensure that calls have two different futex addresses, which allows local users to gain privileges via a crafted FUTEX_REQUEUE command that facilitates unsafe waiter modification. If uaddr == uaddr2, then we have broken the rule of only requeueing from a non-pi futex to a pi futex with this call. If we attempt this, then dangling pointers may be left for rt_waiter resulting in an exploitable condition. This change brings futex_requeue() in line with futex_wait_requeue_pi() which performs the same check as per commit 6f7b0a2a5c0f ("futex: Forbid uaddr == uaddr2 in futex_wait_requeue_pi()") [ tglx: Compare the resulting keys as well, as uaddrs might be different depending on the mapping ] Fixes CVE-2014-3153. -rw-r--r-- kernel/futex.c 25 1 files changed, 25 insertions, 0 deletions diff --git a/kernel/futex.c b/kernel/futex.c index 81dbe77..663ea2b 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -1442,6 +1442,13 @@ static int futex_requeue(u32 __user *uaddr1, unsigned int flags, if (requeue_pi) { /* + * Requeue PI only works on two distinct uaddrs. This + * check is only valid for private futexes. See below. + */ + if (uaddr1 == uaddr2) + return -EINVAL; + + /* * requeue_pi requires a pi_state, try to allocate it now * without any locks in case it fails. */ @@ -1479,6 +1486,15 @@ retry: if (unlikely(ret != 0)) goto out_put_key1; + /* + * The check above which compares uaddrs is not sufficient for + * shared futexes. We need to compare the keys: + */ + if (requeue_pi && match_futex(&key1, &key2)) { + ret = -EINVAL; + goto out_put_keys; + } + hb1 = hash_futex(&key1); hb2 = hash_futex(&key2); @@ -2525,6 +2541,15 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags, if (ret) goto out_key2; + /* + * The check above which compares uaddrs is not sufficient for + * shared futexes. We need to compare the keys: + */ + if (match_futex(&q.key, &key2)) { + ret = -EINVAL; + goto out_put_keys; + } + /* Queue the futex_q, drop the hb lock, wait for wakeup. */ futex_wait_queue_me(hb, &q, to);