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

diff --git a/ipc/msg.c b/ipc/msg.c
index c5d8e3749985be98b17c7bb1183dafb41332ea36..cfc8b388332d92e25629801e1d3123c9b76756cb 100644 (file)
--- 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 89fc354156cb918342751f72e1017727877d86e0..9438ab9027dcac0bdef594e1195784cb8e7e4644 100644 (file)
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -547,12 +547,6 @@ 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;
@@ -562,6 +556,12 @@ 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 27d74e69fd579bbb4dd95b27593c2902df64c0a7..a07ec27e1bfafd8c4bd486bb6ffc6f470c21e1ea 100644 (file)
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -277,6 +277,10 @@ 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);
@@ -289,10 +293,6 @@ 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)