Patch "Initialize msg/shm IPC objects before doing ipc_addid()" has been added to the 4.2-stable tree

This is a note to let you know that I've just added the patch titled

Initialize msg/shm IPC objects before doing ipc_addid()

to the 4.2-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
initialize-msg-shm-ipc-objects-before-doing-ipc_addid.patch
and it can be found in the queue-4.2 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Linus Torvalds <[email protected]>
Date: Wed, 30 Sep 2015 12:48:40 -0400
Subject: Initialize msg/shm IPC objects before doing ipc_addid()

From: Linus Torvalds <[email protected]>

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.

---
 ipc/msg.c  |   14 +++++++-------
 ipc/shm.c  |   13 +++++++------
 ipc/util.c |    8 ++++----
 3 files changed, 18 insertions(+), 17 deletions(-)

@@ -137,13 +137,6 @@ static int newque(struct ipc_namespace *
 		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 *
 	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();
 

@@ -551,12 +551,6 @@ 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;

@@ -565,6 +559,13 @@ 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;
+	}
+
 	list_add(&shp->shm_clist, &current->sysvshm.shm_clist);
 
 	/*

@@ -237,6 +237,10 @@ 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;
+
 	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, struc
 
 	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)

Patches currently in stable-queue which might be from [email protected] are

queue-4.2/x86-efi-fix-boot-crash-by-mapping-efi-memmap-entries-bottom-up-at-runtime-instead-of-top-down.patch queue-4.2/mm-hugetlbfs-skip-shared-vmas-when-unmapping-private-pages-to-satisfy-a-fault.patch queue-4.2/x86-kexec-fix-kexec-crash-in-syscall-kexec_file_load.patch queue-4.2/lib-iommu-common.c-do-not-try-to-deref-a-null-iommu-lazy_flush-pointer-when-n-pool-hint.patch queue-4.2/time-fix-timekeeping_freqadjust-s-incorrect-use-of-abs-instead-of-abs64.patch queue-4.2/perf-x86-intel-fix-constraint-access.patch queue-4.2/ocfs2-dlm-fix-deadlock-when-dispatch-assert-master.patch queue-4.2/locking-qspinlock-x86-only-emit-the-test-and-set-fallback-when-building-guest-support.patch queue-4.2/mm-migrate-hugetlb-putback-destination-hugepage-to-active-list.patch queue-4.2/memcg-fix-dirty-page-migration.patch queue-4.2/arcv2-reduce-clk-for-smp-fpga-configs.patch queue-4.2/locking-qspinlock-x86-fix-performance-regression-under-unaccelerated-vms.patch queue-4.2/x86-mm-set-nx-on-gap-between-__ex_table-and-rodata.patch queue-4.2/initialize-msg-shm-ipc-objects-before-doing-ipc_addid.patch queue-4.2/sched-core-fix-task_dead-race-in-finish_task_switch.patch queue-4.2/tools-lguest-fix-redefinition-of-struct-virtio_pci_cfg_cap.patch queue-4.2/memcg-make-mem_cgroup_read_stat-unsigned.patch queue-4.2/x86-platform-fix-geode-lx-timekeeping-in-the-generic-x86-build.patch