Merge branch 'futexes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip

* 'futexes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  futex: Fix the write access fault problem for real

1 files changed, 24 insertions, 21 deletions

diff --git a/kernel/futex.c b/kernel/futex.c
index 80b5ce716596..1c337112335c 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -284,6 +284,25 @@ void put_futex_key(int fshared, union futex_key *key)
         drop_futex_key_refs(key);
 }
 
+/*
+ * fault_in_user_writeable - fault in user address and verify RW access
+ * @uaddr:      pointer to faulting user space address
+ *
+ * Slow path to fixup the fault we just took in the atomic write
+ * access to @uaddr.
+ *
+ * We have no generic implementation of a non destructive write to the
+ * user address. We know that we faulted in the atomic pagefault
+ * disabled section so we can as well avoid the #PF overhead by
+ * calling get_user_pages() right away.
+ */
+static int fault_in_user_writeable(u32 __user *uaddr)
+{
+        int ret = get_user_pages(current, current->mm, (unsigned long)uaddr,
+                                 sizeof(*uaddr), 1, 0, NULL, NULL);
+        return ret < 0 ? ret : 0;
+}
+
 /**
  * futex_top_waiter() - Return the highest priority waiter on a futex
  * @hb:     the hash bucket the futex_q's reside in
@@ -896,7 +915,6 @@ retry:
 retry_private:
         op_ret = futex_atomic_op_inuser(op, uaddr2);
         if (unlikely(op_ret < 0)) {
-                u32 dummy;
 
                 double_unlock_hb(hb1, hb2);
 
@@ -914,7 +932,7 @@ retry_private:
                         goto out_put_keys;
                 }
 
-                ret = get_user(dummy, uaddr2);
+                ret = fault_in_user_writeable(uaddr2);
                 if (ret)
                         goto out_put_keys;
 
@@ -1204,7 +1222,7 @@ retry_private:
                         double_unlock_hb(hb1, hb2);
                         put_futex_key(fshared, &key2);
                         put_futex_key(fshared, &key1);
-                        ret = get_user(curval2, uaddr2);
+                        ret = fault_in_user_writeable(uaddr2);
                         if (!ret)
                                 goto retry;
                         goto out;
@@ -1482,7 +1500,7 @@ retry:
 handle_fault:
         spin_unlock(q->lock_ptr);
 
-        ret = get_user(uval, uaddr);
+        ret = fault_in_user_writeable(uaddr);
 
         spin_lock(q->lock_ptr);
 
@@ -1807,7 +1825,6 @@ static int futex_lock_pi(u32 __user *uaddr, int fshared,
 {
         struct hrtimer_sleeper timeout, *to = NULL;
         struct futex_hash_bucket *hb;
-        u32 uval;
         struct futex_q q;
         int res, ret;
 
@@ -1909,16 +1926,9 @@ out:
         return ret != -EINTR ? ret : -ERESTARTNOINTR;
 
 uaddr_faulted:
-        /*
-         * We have to r/w  *(int __user *)uaddr, and we have to modify it
-         * atomically.  Therefore, if we continue to fault after get_user()
-         * below, we need to handle the fault ourselves, while still holding
-         * the mmap_sem.  This can occur if the uaddr is under contention as
-         * we have to drop the mmap_sem in order to call get_user().
-         */
         queue_unlock(&q, hb);
 
-        ret = get_user(uval, uaddr);
+        ret = fault_in_user_writeable(uaddr);
         if (ret)
                 goto out_put_key;
 
@@ -2013,17 +2023,10 @@ out:
         return ret;
 
 pi_faulted:
-        /*
-         * We have to r/w  *(int __user *)uaddr, and we have to modify it
-         * atomically.  Therefore, if we continue to fault after get_user()
-         * below, we need to handle the fault ourselves, while still holding
-         * the mmap_sem.  This can occur if the uaddr is under contention as
-         * we have to drop the mmap_sem in order to call get_user().
-         */
         spin_unlock(&hb->lock);
         put_futex_key(fshared, &key);
 
-        ret = get_user(uval, uaddr);
+        ret = fault_in_user_writeable(uaddr);
         if (!ret)
                 goto retry;