[3.13.y-ckt stable] Patch "Initialize msg/shm IPC objects before doing ipc_addid()" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    Initialize msg/shm IPC objects before doing ipc_addid()

to the linux-3.13.y-queue branch of the 3.13.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11-ckt30.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From a8129adb03f172d0e01b744763f768ff6d5f095a Mon Sep 17 00:00:00 2001
From: Linus Torvalds <torvalds at linux-foundation.org>
Date: Wed, 30 Sep 2015 12:48:40 -0400
Subject: Initialize msg/shm IPC objects before doing ipc_addid()

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 at google.com>
Cc: Manfred Spraul <manfred at colorfullife.com>
Cc: Davidlohr Bueso <dbueso at suse.de>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>

Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 ipc/msg.c  | 14 +++++++-------
 ipc/shm.c  | 12 ++++++------
 ipc/util.c |  8 ++++----
 3 files changed, 17 insertions(+), 17 deletions(-)

diff --git a/ipc/msg.c b/ipc/msg.c
index 52770bf..32aaaab 100644
--- a/ipc/msg.c
+++ b/ipc/msg.c
@@ -202,13 +202,6 @@ 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;
@@ -218,6 +211,13 @@ 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 7a51443..ff850da 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -544,12 +544,6 @@ 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;
@@ -559,6 +553,12 @@ static int newseg(struct ipc_namespace *ns, struct ipc_params *params)
 	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.
diff --git a/ipc/util.c b/ipc/util.c
index 3ae17a4..cdaf404 100644
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -290,6 +290,10 @@ 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);
@@ -302,10 +306,6 @@ 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 > ids->seq_max)
--
1.9.1