[PATCH 3.13 206/212] futex-prevent-requeue-pi-on-same-futex.patch futex: Forbid uaddr == uaddr2 in futex_requeue(..., requeue_pi=1)

Kamal Mostafa
2014-06-17T21:45:00Z

From: Thomas Gleixner <tglx@linutronix.de>

commit e9c243a5a6de0be8e584c604d353412584b592f8 upstream.

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.

Reported-by: Pinkie Pie
Signed-off-by: Will Drewry <wad@chromium.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Darren Hart <dvhart@linux.intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
kernel/futex.c | 25 +++++++++++++++++++++++++
1 file changed, 25 insertions(+)

diff --git a/kernel/futex.c b/kernel/futex.c
index 7876c15..c861191 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1295,6 +1295,13 @@ 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.
*/
@@ -1332,6 +1339,15 @@ 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);

@@ -2362,6 +2378,15 @@ 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);

--
1.9.1