ipc: move locking out of ipcctl_pre_down_nolock

commit 7b4cc5d8411bd4e9d61d8714f53859740cf830c2 upstream.

This function currently acquires both the rw_mutex and the rcu lock on
successful lookups, leaving the callers to explicitly unlock them,
creating another two level locking situation.

Make the callers (including those that still use ipcctl_pre_down())
explicitly lock and unlock the rwsem and rcu lock.

Signed-off-by: Davidlohr Bueso <davidlohr.bueso@hp.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 17 insertions, 7 deletions

diff --git a/ipc/msg.c b/ipc/msg.c
index 56bff33457b2..6c1609d572cc 100644
--- a/ipc/msg.c
+++ b/ipc/msg.c
@@ -407,31 +407,38 @@ static int msgctl_down(struct ipc_namespace *ns, int msqid, int cmd,
                         return -EFAULT;
         }
 
+        down_write(&msg_ids(ns).rw_mutex);
+        rcu_read_lock();
+
         ipcp = ipcctl_pre_down(ns, &msg_ids(ns), msqid, cmd,
                                &msqid64.msg_perm, msqid64.msg_qbytes);
-        if (IS_ERR(ipcp))
-                return PTR_ERR(ipcp);
+        if (IS_ERR(ipcp)) {
+                err = PTR_ERR(ipcp);
+                /* the ipc lock is not held upon failure */
+                goto out_unlock1;
+        }
 
         msq = container_of(ipcp, struct msg_queue, q_perm);
 
         err = security_msg_queue_msgctl(msq, cmd);
         if (err)
-                goto out_unlock;
+                goto out_unlock0;
 
         switch (cmd) {
         case IPC_RMID:
+                /* freeque unlocks the ipc object and rcu */
                 freeque(ns, ipcp);
                 goto out_up;
         case IPC_SET:
                 if (msqid64.msg_qbytes > ns->msg_ctlmnb &&
                     !capable(CAP_SYS_RESOURCE)) {
                         err = -EPERM;
-                        goto out_unlock;
+                        goto out_unlock0;
                 }
 
                 err = ipc_update_perm(&msqid64.msg_perm, ipcp);
                 if (err)
-                        goto out_unlock;
+                        goto out_unlock0;
 
                 msq->q_qbytes = msqid64.msg_qbytes;
 
@@ -448,8 +455,11 @@ static int msgctl_down(struct ipc_namespace *ns, int msqid, int cmd,
         default:
                 err = -EINVAL;
         }
-out_unlock:
-        msg_unlock(msq);
+
+out_unlock0:
+        ipc_unlock_object(&msq->q_perm);
+out_unlock1:
+        rcu_read_unlock();
 out_up:
         up_write(&msg_ids(ns).rw_mutex);
         return err;