[PATCH 3.2 094/107] Initialize msg/shm IPC objects before doing ipc_addid()

[Ben Hutchings]

3.2.72-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>

commit b9a532277938798b53178d5a66af6e2915cb27cf upstream.

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@xxxxxxxxxx>
Cc: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
Cc: Davidlohr Bueso <dbueso@xxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
[bwh: Backported to 3.2:
 - Adjust context
 - The error path being moved looks a little different]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
--- a/ipc/msg.c
+++ b/ipc/msg.c
@@ -198,6 +198,15 @@ static int newque(struct ipc_namespace *
 		return retval;
 	}
 
+	msq->q_stime = msq->q_rtime = 0;
+	msq->q_ctime = get_seconds();
+	msq->q_cbytes = msq->q_qnum = 0;
+	msq->q_qbytes = ns->msg_ctlmnb;
+	msq->q_lspid = msq->q_lrpid = 0;
+	INIT_LIST_HEAD(&msq->q_messages);
+	INIT_LIST_HEAD(&msq->q_receivers);
+	INIT_LIST_HEAD(&msq->q_senders);
+
 	/*
 	 * ipc_addid() locks msq
 	 */
@@ -208,15 +217,6 @@ static int newque(struct ipc_namespace *
 		return id;
 	}
 
-	msq->q_stime = msq->q_rtime = 0;
-	msq->q_ctime = get_seconds();
-	msq->q_cbytes = msq->q_qnum = 0;
-	msq->q_qbytes = ns->msg_ctlmnb;
-	msq->q_lspid = msq->q_lrpid = 0;
-	INIT_LIST_HEAD(&msq->q_messages);
-	INIT_LIST_HEAD(&msq->q_receivers);
-	INIT_LIST_HEAD(&msq->q_senders);
-
 	msg_unlock(msq);
 
 	return msq->q_perm.id;
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -498,12 +498,6 @@ static int newseg(struct ipc_namespace *
 	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;
@@ -512,6 +506,13 @@ static int newseg(struct ipc_namespace *
 	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;
+	}
+
 	/*
 	 * shmid gets reported as "inode#" in /proc/pid/maps.
 	 * proc-ps tools use this. Changing this will break them.
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -264,6 +264,10 @@ int ipc_addid(struct ipc_ids* ids, struc
 	rcu_read_lock();
 	spin_lock(&new->lock);
 
+	current_euid_egid(&euid, &egid);
+	new->cuid = new->uid = euid;
+	new->gid = new->cgid = egid;
+
 	err = idr_get_new(&ids->ipcs_idr, new, &id);
 	if (err) {
 		spin_unlock(&new->lock);
@@ -273,10 +277,6 @@ int ipc_addid(struct ipc_ids* ids, struc
 
 	ids->in_use++;
 
-	current_euid_egid(&euid, &egid);
-	new->cuid = new->uid = euid;
-	new->gid = new->cgid = egid;
-
 	new->seq = ids->seq++;
 	if(ids->seq > ids->seq_max)
 		ids->seq = 0;

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