diff --git a/ipc/shm.c b/ipc/shm.c
index 3818fae..65c3a29 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -111,6 +111,7 @@
 void shm_exit_ns(struct ipc_namespace *ns)
 {
 	struct shmid_kernel *shp;
+	struct kern_ipc_perm *perm;
 	int next_id;
 	int total, in_use;
 
@@ -119,10 +120,11 @@
 	in_use = shm_ids(ns).in_use;
 
 	for (total = 0, next_id = 0; total < in_use; next_id++) {
-		shp = idr_find(&shm_ids(ns).ipcs_idr, next_id);
-		if (shp == NULL)
+		perm = idr_find(&shm_ids(ns).ipcs_idr, next_id);
+		if (perm == NULL)
 			continue;
-		ipc_lock_by_ptr(&shp->shm_perm);
+		ipc_lock_by_ptr(perm);
+		shp = container_of(perm, struct shmid_kernel, shm_perm);
 		do_shm_rmid(ns, shp);
 		total++;
 	}
@@ -149,6 +151,9 @@
 {
 	struct kern_ipc_perm *ipcp = ipc_lock_down(&shm_ids(ns), id);
 
+	if (IS_ERR(ipcp))
+		return (struct shmid_kernel *)ipcp;
+
 	return container_of(ipcp, struct shmid_kernel, shm_perm);
 }
 
@@ -158,6 +163,9 @@
 {
 	struct kern_ipc_perm *ipcp = ipc_lock_check_down(&shm_ids(ns), id);
 
+	if (IS_ERR(ipcp))
+		return (struct shmid_kernel *)ipcp;
+
 	return container_of(ipcp, struct shmid_kernel, shm_perm);
 }
 
@@ -169,6 +177,9 @@
 {
 	struct kern_ipc_perm *ipcp = ipc_lock(&shm_ids(ns), id);
 
+	if (IS_ERR(ipcp))
+		return (struct shmid_kernel *)ipcp;
+
 	return container_of(ipcp, struct shmid_kernel, shm_perm);
 }
 
@@ -177,6 +188,9 @@
 {
 	struct kern_ipc_perm *ipcp = ipc_lock_check(&shm_ids(ns), id);
 
+	if (IS_ERR(ipcp))
+		return (struct shmid_kernel *)ipcp;
+
 	return container_of(ipcp, struct shmid_kernel, shm_perm);
 }