ipc: move locking out of ipcctl_pre_down_nolock

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>

1 files changed, 17 insertions, 6 deletions

diff --git a/ipc/shm.c b/ipc/shm.c
index e7d51072d1c7..c6b4ad5ce3b7 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -757,31 +757,42 @@ static int shmctl_down(struct ipc_namespace *ns, int shmid, int cmd,
                         return -EFAULT;
         }
 
+        down_write(&shm_ids(ns).rw_mutex);
+        rcu_read_lock();
+
         ipcp = ipcctl_pre_down(ns, &shm_ids(ns), shmid, cmd,
                                &shmid64.shm_perm, 0);
-        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;
+        }
 
         shp = container_of(ipcp, struct shmid_kernel, shm_perm);
 
         err = security_shm_shmctl(shp, cmd);
         if (err)
-                goto out_unlock;
+                goto out_unlock0;
+
         switch (cmd) {
         case IPC_RMID:
+                /* do_shm_rmid unlocks the ipc object and rcu */
                 do_shm_rmid(ns, ipcp);
                 goto out_up;
         case IPC_SET:
                 err = ipc_update_perm(&shmid64.shm_perm, ipcp);
                 if (err)
-                        goto out_unlock;
+                        goto out_unlock0;
                 shp->shm_ctim = get_seconds();
                 break;
         default:
                 err = -EINVAL;
         }
-out_unlock:
-        shm_unlock(shp);
+
+out_unlock0:
+        ipc_unlock_object(&shp->shm_perm);
+out_unlock1:
+        rcu_read_unlock();
 out_up:
         up_write(&shm_ids(ns).rw_mutex);
         return err;