From Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Commit: 7fb9d98d427d9764eb7bf534addf273a58c5f656
Date: Tue, 3 Jun 2014 12:27:06 +0000
Subject: [PATCH 1/4] futex-prevent-requeue-pi-on-same-futex.patch futex:
Forbid uaddr == uaddr2 in futex_requeue(..., requeue_pi=1)
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() into line with
futex_wait_requeue_pi() which performs the same check as per commit
6f7b0a2a5 (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.
Reported-by: Pinkie Pie
Signed-off-by: Will Drewry <wad@xxxxxxxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
kernel/futex.c | 25 +++++++++++++++++++++++++
1 files changed, 25 insertions(+), 0 deletions(-)
diff --git a/kernel/futex.c b/kernel/futex.c
index baece19..e67c01d 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1409,6 +1409,13 @@ 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.
*/
@@ -1446,6 +1453,15 @@ 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);
@@ -2481,6 +2497,15 @@ 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);
--
1.7.1
--
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