futex-prevent-requeue-pi-on-same-futex.patch futex: Forbid uaddr == uaddr2 in futex_r...

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.

Change-Id: I8ea4f0601e6e4c881197c88d5afb1ce802a2144c
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>

diff --git a/kernel/futex.c b/kernel/futex.c
index d8347b7a064f8b1c0e7e99bcd29e927637880762..553c383e9e34722f1ba85d5199be7312d4b44080 100644 (file)
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1277,6 +1277,13 @@ static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
        u32 curval2;
 
        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.
@@ -1315,6 +1322,15 @@ 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);
 
@@ -2336,6 +2352,15 @@ 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);