Initialize msg/shm IPC objects before doing ipc_addid()

As reported by Dmitry Vyukov, we really shouldn't do ipc_addid() before
having initialized the IPC object state.  Yes, we initialize the IPC
object in a locked state, but with all the lockless RCU lookup work,
that IPC object lock no longer means that the state cannot be seen.

We already did this for the IPC semaphore code (see commit e8577d1f0329:
"ipc/sem.c: fully initialize sem_array before making it visible") but we
clearly forgot about msg and shm.

Reported-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Manfred Spraul <manfred@colorfullife.com>
Cc: Davidlohr Bueso <dbueso@suse.de>
Cc: stable@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 18 insertions, 17 deletions

diff --git a/ipc/msg.c b/ipc/msg.c
index 66c4f567eb73..1471db9a7e61 100644
--- a/ipc/msg.c
+++ b/ipc/msg.c
@@ -137,13 +137,6 @@ static int newque(struct ipc_namespace *ns, struct ipc_params *params)
                 return retval;
         }
 
-        /* ipc_addid() locks msq upon success. */
-        id = ipc_addid(&msg_ids(ns), &msq->q_perm, ns->msg_ctlmni);
-        if (id < 0) {
-                ipc_rcu_putref(msq, msg_rcu_free);
-                return id;
-        }
-
         msq->q_stime = msq->q_rtime = 0;
         msq->q_ctime = get_seconds();
         msq->q_cbytes = msq->q_qnum = 0;
@@ -153,6 +146,13 @@ static int newque(struct ipc_namespace *ns, struct ipc_params *params)
         INIT_LIST_HEAD(&msq->q_receivers);
         INIT_LIST_HEAD(&msq->q_senders);
 
+        /* ipc_addid() locks msq upon success. */
+        id = ipc_addid(&msg_ids(ns), &msq->q_perm, ns->msg_ctlmni);
+        if (id < 0) {
+                ipc_rcu_putref(msq, msg_rcu_free);
+                return id;
+        }
+
         ipc_unlock_object(&msq->q_perm);
         rcu_read_unlock();
 
diff --git a/ipc/shm.c b/ipc/shm.c
index 222131e8e38f..41787276e141 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -551,12 +551,6 @@ static int newseg(struct ipc_namespace *ns, struct ipc_params *params)
         if (IS_ERR(file))
                 goto no_file;
 
-        id = ipc_addid(&shm_ids(ns), &shp->shm_perm, ns->shm_ctlmni);
-        if (id < 0) {
-                error = id;
-                goto no_id;
-        }
-
         shp->shm_cprid = task_tgid_vnr(current);
         shp->shm_lprid = 0;
         shp->shm_atim = shp->shm_dtim = 0;
@@ -565,6 +559,13 @@ static int newseg(struct ipc_namespace *ns, struct ipc_params *params)
         shp->shm_nattch = 0;
         shp->shm_file = file;
         shp->shm_creator = current;
+
+        id = ipc_addid(&shm_ids(ns), &shp->shm_perm, ns->shm_ctlmni);
+        if (id < 0) {
+                error = id;
+                goto no_id;
+        }
+
         list_add(&shp->shm_clist, &current->sysvshm.shm_clist);
 
         /*
diff --git a/ipc/util.c b/ipc/util.c
index be4230020a1f..0f401d94b7c6 100644
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -237,6 +237,10 @@ int ipc_addid(struct ipc_ids *ids, struct kern_ipc_perm *new, int size)
         rcu_read_lock();
         spin_lock(&new->lock);
 
+        current_euid_egid(&euid, &egid);
+        new->cuid = new->uid = euid;
+        new->gid = new->cgid = egid;
+
         id = idr_alloc(&ids->ipcs_idr, new,
                        (next_id < 0) ? 0 : ipcid_to_idx(next_id), 0,
                        GFP_NOWAIT);
@@ -249,10 +253,6 @@ int ipc_addid(struct ipc_ids *ids, struct kern_ipc_perm *new, int size)
 
         ids->in_use++;
 
-        current_euid_egid(&euid, &egid);
-        new->cuid = new->uid = euid;
-        new->gid = new->cgid = egid;
-
         if (next_id < 0) {
                 new->seq = ids->seq++;
                 if (ids->seq > IPCID_SEQ_MAX)