1 files changed, 34 insertions, 13 deletions

diff --git a/kernel/futex.c b/kernel/futex.c
index 5f589279e462..7c68225e3967 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -745,7 +745,8 @@ void exit_pi_state_list(struct task_struct *curr)
 
 static int
 lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
-                union futex_key *key, struct futex_pi_state **ps)
+                union futex_key *key, struct futex_pi_state **ps,
+                struct task_struct *task)
 {
         struct futex_pi_state *pi_state = NULL;
         struct futex_q *this, *next;
@@ -786,6 +787,16 @@ lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
                                         return -EINVAL;
                         }
 
+                        /*
+                         * Protect against a corrupted uval. If uval
+                         * is 0x80000000 then pid is 0 and the waiter
+                         * bit is set. So the deadlock check in the
+                         * calling code has failed and we did not fall
+                         * into the check above due to !pid.
+                         */
+                        if (task && pi_state->owner == task)
+                                return -EDEADLK;
+
                         atomic_inc(&pi_state->refcount);
                         *ps = pi_state;
 
@@ -935,7 +946,7 @@ retry:
          * We dont have the lock. Look up the PI state (or create it if
          * we are the first waiter):
          */
-        ret = lookup_pi_state(uval, hb, key, ps);
+        ret = lookup_pi_state(uval, hb, key, ps, task);
 
         if (unlikely(ret)) {
                 switch (ret) {
@@ -1347,7 +1358,7 @@ void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
  *
  * Return:
  *  0 - failed to acquire the lock atomically;
- *  1 - acquired the lock;
+ * >0 - acquired the lock, return value is vpid of the top_waiter
  * <0 - error
  */
 static int futex_proxy_trylock_atomic(u32 __user *pifutex,
@@ -1358,7 +1369,7 @@ static int futex_proxy_trylock_atomic(u32 __user *pifutex,
 {
         struct futex_q *top_waiter = NULL;
         u32 curval;
-        int ret;
+        int ret, vpid;
 
         if (get_futex_value_locked(&curval, pifutex))
                 return -EFAULT;
@@ -1386,11 +1397,13 @@ static int futex_proxy_trylock_atomic(u32 __user *pifutex,
          * the contended case or if set_waiters is 1.  The pi_state is returned
          * in ps in contended cases.
          */
+        vpid = task_pid_vnr(top_waiter->task);
         ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
                                    set_waiters);
-        if (ret == 1)
+        if (ret == 1) {
                 requeue_pi_wake_futex(top_waiter, key2, hb2);
-
+                return vpid;
+        }
         return ret;
 }
 
@@ -1421,7 +1434,6 @@ static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
         struct futex_pi_state *pi_state = NULL;
         struct futex_hash_bucket *hb1, *hb2;
         struct futex_q *this, *next;
-        u32 curval2;
 
         if (requeue_pi) {
                 /*
@@ -1509,16 +1521,25 @@ retry_private:
                  * At this point the top_waiter has either taken uaddr2 or is
                  * waiting on it.  If the former, then the pi_state will not
                  * exist yet, look it up one more time to ensure we have a
-                 * reference to it.
+                 * reference to it. If the lock was taken, ret contains the
+                 * vpid of the top waiter task.
                  */
-                if (ret == 1) {
+                if (ret > 0) {
                         WARN_ON(pi_state);
                         drop_count++;
                         task_count++;
-                        ret = get_futex_value_locked(&curval2, uaddr2);
-                        if (!ret)
-                                ret = lookup_pi_state(curval2, hb2, &key2,
-                                                      &pi_state);
+                        /*
+                         * If we acquired the lock, then the user
+                         * space value of uaddr2 should be vpid. It
+                         * cannot be changed by the top waiter as it
+                         * is blocked on hb2 lock if it tries to do
+                         * so. If something fiddled with it behind our
+                         * back the pi state lookup might unearth
+                         * it. So we rather use the known value than
+                         * rereading and handing potential crap to
+                         * lookup_pi_state.
+                         */
+                        ret = lookup_pi_state(ret, hb2, &key2, &pi_state, NULL);
                 }
 
                 switch (ret) {