linux-kernel - [PATCH 3.19.y-ckt 017/155] Initialize msg/shm IPC objects before doing ipc

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Message-Id: <1447370309-357-18-git-send-email-kamal@canonical.com>
Date:	Thu, 12 Nov 2015 15:16:11 -0800
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Manfred Spraul <manfred@...orfullife.com>,
	Davidlohr Bueso <dbueso@...e.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 3.19.y-ckt 017/155] Initialize msg/shm IPC objects before doing ipc_addid()

3.19.8-ckt10 -stable review patch.  If anyone has any objections, please let me know.

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

From: Linus Torvalds <torvalds@...ux-foundation.org>

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@...gle.com>
Cc: Manfred Spraul <manfred@...orfullife.com>
Cc: Davidlohr Bueso <dbueso@...e.de>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
 ipc/msg.c  | 14 +++++++-------
 ipc/shm.c  | 13 +++++++------
 ipc/util.c |  8 ++++----
 3 files changed, 18 insertions(+), 17 deletions(-)

diff --git a/ipc/msg.c b/ipc/msg.c
index a7261d5..1b8f36f 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 19633b4..dd5f686 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -550,12 +550,6 @@ 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;
@@ -564,6 +558,13 @@ 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 106bed0..372dd6ec 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)
-- 
1.9.1

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