[PATCH] ipc/sem.c: Fully initialize sem_array before making it visible

[Manfred Spraul]

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.

Reported-by: Rik van Riel <riel@xxxxxxxxxx>
Signed-off-by: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
---
 ipc/sem.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/ipc/sem.c b/ipc/sem.c
index 454f6c6..53c3310 100644
--- 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();
 
-- 
1.9.3


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