ipc: move locking out of ipcctl_pre_down_nolock

This function currently acquires both the rw_mutex and the rcu lock on
successful lookups, leaving the callers to explicitly unlock them,
creating another two level locking situation.

Make the callers (including those that still use ipcctl_pre_down())
explicitly lock and unlock the rwsem and rcu lock.

Signed-off-by: Davidlohr Bueso <davidlohr.bueso@hp.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

4 files changed, 56 insertions, 39 deletions

diff --git a/ipc/msg.c b/ipc/msg.c
index 7a3d6aab369d..f62fa5eed847 100644
--- a/ipc/msg.c
+++ b/ipc/msg.c
@@ -407,31 +407,38 @@ static int msgctl_down(struct ipc_namespace *ns, int msqid, int cmd,
                         return -EFAULT;
         }
 
+        down_write(&msg_ids(ns).rw_mutex);
+        rcu_read_lock();
+
         ipcp = ipcctl_pre_down(ns, &msg_ids(ns), msqid, cmd,
                                &msqid64.msg_perm, msqid64.msg_qbytes);
-        if (IS_ERR(ipcp))
-                return PTR_ERR(ipcp);
+        if (IS_ERR(ipcp)) {
+                err = PTR_ERR(ipcp);
+                /* the ipc lock is not held upon failure */
+                goto out_unlock1;
+        }
 
         msq = container_of(ipcp, struct msg_queue, q_perm);
 
         err = security_msg_queue_msgctl(msq, cmd);
         if (err)
-                goto out_unlock;
+                goto out_unlock0;
 
         switch (cmd) {
         case IPC_RMID:
+                /* freeque unlocks the ipc object and rcu */
                 freeque(ns, ipcp);
                 goto out_up;
         case IPC_SET:
                 if (msqid64.msg_qbytes > ns->msg_ctlmnb &&
                     !capable(CAP_SYS_RESOURCE)) {
                         err = -EPERM;
-                        goto out_unlock;
+                        goto out_unlock0;
                 }
 
                 err = ipc_update_perm(&msqid64.msg_perm, ipcp);
                 if (err)
-                        goto out_unlock;
+                        goto out_unlock0;
 
                 msq->q_qbytes = msqid64.msg_qbytes;
 
@@ -448,8 +455,11 @@ static int msgctl_down(struct ipc_namespace *ns, int msqid, int cmd,
         default:
                 err = -EINVAL;
         }
-out_unlock:
-        msg_unlock(msq);
+
+out_unlock0:
+        ipc_unlock_object(&msq->q_perm);
+out_unlock1:
+        rcu_read_unlock();
 out_up:
         up_write(&msg_ids(ns).rw_mutex);
         return err;
diff --git a/ipc/sem.c b/ipc/sem.c
index 92ec6c69bab5..b4b892b5c5f8 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -1289,39 +1289,44 @@ static int semctl_down(struct ipc_namespace *ns, int semid,
                         return -EFAULT;
         }
 
+        down_write(&sem_ids(ns).rw_mutex);
+        rcu_read_lock();
+
         ipcp = ipcctl_pre_down_nolock(ns, &sem_ids(ns), semid, cmd,
                                       &semid64.sem_perm, 0);
-        if (IS_ERR(ipcp))
-                return PTR_ERR(ipcp);
+        if (IS_ERR(ipcp)) {
+                err = PTR_ERR(ipcp);
+                /* the ipc lock is not held upon failure */
+                goto out_unlock1;
+        }
 
         sma = container_of(ipcp, struct sem_array, sem_perm);
 
         err = security_sem_semctl(sma, cmd);
-        if (err) {
-                rcu_read_unlock();
-                goto out_up;
-        }
+        if (err)
+                goto out_unlock1;
 
-        switch(cmd){
+        switch (cmd) {
         case IPC_RMID:
                 sem_lock(sma, NULL, -1);
+                /* freeary unlocks the ipc object and rcu */
                 freeary(ns, ipcp);
                 goto out_up;
         case IPC_SET:
                 sem_lock(sma, NULL, -1);
                 err = ipc_update_perm(&semid64.sem_perm, ipcp);
                 if (err)
-                        goto out_unlock;
+                        goto out_unlock0;
                 sma->sem_ctime = get_seconds();
                 break;
         default:
-                rcu_read_unlock();
                 err = -EINVAL;
-                goto out_up;
+                goto out_unlock1;
         }
 
-out_unlock:
+out_unlock0:
         sem_unlock(sma, -1);
+out_unlock1:
         rcu_read_unlock();
 out_up:
         up_write(&sem_ids(ns).rw_mutex);
diff --git a/ipc/shm.c b/ipc/shm.c
index e7d51072d1c7..c6b4ad5ce3b7 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -757,31 +757,42 @@ static int shmctl_down(struct ipc_namespace *ns, int shmid, int cmd,
                         return -EFAULT;
         }
 
+        down_write(&shm_ids(ns).rw_mutex);
+        rcu_read_lock();
+
         ipcp = ipcctl_pre_down(ns, &shm_ids(ns), shmid, cmd,
                                &shmid64.shm_perm, 0);
-        if (IS_ERR(ipcp))
-                return PTR_ERR(ipcp);
+        if (IS_ERR(ipcp)) {
+                err = PTR_ERR(ipcp);
+                /* the ipc lock is not held upon failure */
+                goto out_unlock1;
+        }
 
         shp = container_of(ipcp, struct shmid_kernel, shm_perm);
 
         err = security_shm_shmctl(shp, cmd);
         if (err)
-                goto out_unlock;
+                goto out_unlock0;
+
         switch (cmd) {
         case IPC_RMID:
+                /* do_shm_rmid unlocks the ipc object and rcu */
                 do_shm_rmid(ns, ipcp);
                 goto out_up;
         case IPC_SET:
                 err = ipc_update_perm(&shmid64.shm_perm, ipcp);
                 if (err)
-                        goto out_unlock;
+                        goto out_unlock0;
                 shp->shm_ctim = get_seconds();
                 break;
         default:
                 err = -EINVAL;
         }
-out_unlock:
-        shm_unlock(shp);
+
+out_unlock0:
+        ipc_unlock_object(&shp->shm_perm);
+out_unlock1:
+        rcu_read_unlock();
 out_up:
         up_write(&shm_ids(ns).rw_mutex);
         return err;
diff --git a/ipc/util.c b/ipc/util.c
index 399821ac0a9a..a0c139f3d1f3 100644
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -746,8 +746,10 @@ int ipc_update_perm(struct ipc64_perm *in, struct kern_ipc_perm *out)
  * It must be called without any lock held and
  *  - retrieves the ipc with the given id in the given table.
  *  - performs some audit and permission check, depending on the given cmd
- *  - returns the ipc with both ipc and rw_mutex locks held in case of success
+ *  - returns the ipc with the ipc lock held in case of success
  *    or an err-code without any lock held otherwise.
+ *
+ * Call holding the both the rw_mutex and the rcu read lock.
  */
 struct kern_ipc_perm *ipcctl_pre_down(struct ipc_namespace *ns,
                                       struct ipc_ids *ids, int id, int cmd,
@@ -772,13 +774,10 @@ struct kern_ipc_perm *ipcctl_pre_down_nolock(struct ipc_namespace *ns,
         int err = -EPERM;
         struct kern_ipc_perm *ipcp;
 
-        down_write(&ids->rw_mutex);
-        rcu_read_lock();
-
         ipcp = ipc_obtain_object_check(ids, id);
         if (IS_ERR(ipcp)) {
                 err = PTR_ERR(ipcp);
-                goto out_up;
+                goto err;
         }
 
         audit_ipc_obj(ipcp);
@@ -789,16 +788,8 @@ struct kern_ipc_perm *ipcctl_pre_down_nolock(struct ipc_namespace *ns,
         euid = current_euid();
         if (uid_eq(euid, ipcp->cuid) || uid_eq(euid, ipcp->uid)  ||
             ns_capable(ns->user_ns, CAP_SYS_ADMIN))
-                return ipcp;
-
-out_up:
-        /*
-         * Unsuccessful lookup, unlock and return
-         * the corresponding error.
-         */
-        rcu_read_unlock();
-        up_write(&ids->rw_mutex);
-
+                return ipcp; /* successful lookup */
+err:
         return ERR_PTR(err);
 }