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

Pull core futex/rtmutex fixes from Thomas Gleixner:
 "Three fixlets for long standing issues in the futex/rtmutex code
  unearthed by Dave Jones syscall fuzzer:

   - Add missing early deadlock detection checks in the futex code
   - Prevent user space from attaching a futex to kernel threads
   - Make the deadlock detector of rtmutex work again

  Looks large, but is more comments than code change"

* 'core-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  rtmutex: Fix deadlock detector for real
  futex: Prevent attaching to kernel threads
  futex: Add another early deadlock detection check

2 files changed, 67 insertions, 17 deletions

diff --git a/kernel/futex.c b/kernel/futex.c
index 5f589279e462..81dbe773ce4c 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;
 
@@ -803,6 +814,11 @@ lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
         if (!p)
                 return -ESRCH;
 
+        if (!p->mm) {
+                put_task_struct(p);
+                return -EPERM;
+        }
+
         /*
          * We need to look at the task state flags to figure out,
          * whether the task is exiting. To protect against the do_exit
@@ -935,7 +951,7 @@ 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 +1363,7 @@ 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 +1374,7 @@ 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 +1402,13 @@ 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 +1439,6 @@ 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 +1526,25 @@ 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) {
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index aa4dff04b594..a620d4d08ca6 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -343,9 +343,16 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
          * top_waiter can be NULL, when we are in the deboosting
          * mode!
          */
-        if (top_waiter && (!task_has_pi_waiters(task) ||
-                           top_waiter != task_top_pi_waiter(task)))
-                goto out_unlock_pi;
+        if (top_waiter) {
+                if (!task_has_pi_waiters(task))
+                        goto out_unlock_pi;
+                /*
+                 * If deadlock detection is off, we stop here if we
+                 * are not the top pi waiter of the task.
+                 */
+                if (!detect_deadlock && top_waiter != task_top_pi_waiter(task))
+                        goto out_unlock_pi;
+        }
 
         /*
          * When deadlock detection is off then we check, if further
@@ -361,7 +368,12 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
                 goto retry;
         }
 
-        /* Deadlock detection */
+        /*
+         * Deadlock detection. If the lock is the same as the original
+         * lock which caused us to walk the lock chain or if the
+         * current lock is owned by the task which initiated the chain
+         * walk, we detected a deadlock.
+         */
         if (lock == orig_lock || rt_mutex_owner(lock) == top_task) {
                 debug_rt_mutex_deadlock(deadlock_detect, orig_waiter, lock);
                 raw_spin_unlock(&lock->wait_lock);
@@ -527,6 +539,18 @@ static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
         unsigned long flags;
         int chain_walk = 0, res;
 
+        /*
+         * Early deadlock detection. We really don't want the task to
+         * enqueue on itself just to untangle the mess later. It's not
+         * only an optimization. We drop the locks, so another waiter
+         * can come in before the chain walk detects the deadlock. So
+         * the other will detect the deadlock and return -EDEADLOCK,
+         * which is wrong, as the other waiter is not in a deadlock
+         * situation.
+         */
+        if (detect_deadlock && owner == task)
+                return -EDEADLK;
+
         raw_spin_lock_irqsave(&task->pi_lock, flags);
         __rt_mutex_adjust_prio(task);
         waiter->task = task;