[RHEL7.1 CVE PATCH 1/4] futex-prevent-requeue-pi-on-same-futex.patch futex

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 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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