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() 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>
Cc: stable@vger.kernel.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>

1 files changed, 25 insertions, 0 deletions

diff --git a/kernel/futex.c b/kernel/futex.c
index 81dbe773ce4c..663ea2b84a38 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);