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Subject[GIT pull] futex fixes for 2.6.31
Linus,

Please pull the latest futexes-for-linus git tree from:

git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip.git futexes-for-linus

Thanks,

tglx

------------------>
Thomas Gleixner (1):
futex: Fix the write access fault problem for real


kernel/futex.c | 45 ++++++++++++++++++++++++---------------------
1 files changed, 24 insertions(+), 21 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index 80b5ce7..1c33711 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;


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