ipc/sem.c: fully initialize sem_array before making it visible

ipc_addid() makes a new ipc identifier visible to everyone.  New objects
start as locked, so that the caller can complete the initialization
after the call.  Within struct sem_array, at least sma->sem_base and
sma->sem_nsems are accessed without any locks, therefore this approach
doesn't work.

Thus: Move the ipc_addid() to the end of the initialization.

Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Reported-by: Rik van Riel <riel@redhat.com>
Acked-by: Rik van Riel <riel@redhat.com>
Acked-by: Davidlohr Bueso <dave@stgolabs.net>
Acked-by: Rafael Aquini <aquini@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/ipc/sem.c b/ipc/sem.c
index 454f6c6..53c3310 100644 (file)
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -507,13 +507,6 @@ static int newary(struct ipc_namespace *ns, struct ipc_params *params)
                return retval;
        }
 
-       id = ipc_addid(&sem_ids(ns), &sma->sem_perm, ns->sc_semmni);
-       if (id < 0) {
-               ipc_rcu_putref(sma, sem_rcu_free);
-               return id;
-       }
-       ns->used_sems += nsems;
-
        sma->sem_base = (struct sem *) &sma[1];
 
        for (i = 0; i < nsems; i++) {
@@ -528,6 +521,14 @@ static int newary(struct ipc_namespace *ns, struct ipc_params *params)
        INIT_LIST_HEAD(&sma->list_id);
        sma->sem_nsems = nsems;
        sma->sem_ctime = get_seconds();
+
+       id = ipc_addid(&sem_ids(ns), &sma->sem_perm, ns->sc_semmni);
+       if (id < 0) {
+               ipc_rcu_putref(sma, sem_rcu_free);
+               return id;
+       }
+       ns->used_sems += nsems;
+
        sem_unlock(sma, -1);
        rcu_read_unlock();