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>

diff --git a/ipc/msg.c b/ipc/msg.c
index 7a3d6aab369d256ec508d58620e2f668a99e4f62..f62fa5eed8471303b37707b88417666a0e479fb5 100644 (file)
--- 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 92ec6c69bab51880aa55f175e519f5fc0cf329d6..b4b892b5c5f8d6124c478ae10c0dcdce94b56358 100644 (file)
--- 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 e7d51072d1c708f087f8a979adcaa6b9beb97839..c6b4ad5ce3b7b53df40b5934bb823fff4de9f9c8 100644 (file)
--- 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 399821ac0a9a9c6c67af1a448bc7268d70fe85a2..a0c139f3d1f3ea0ef62b25939db8d30ff52d41c3 100644 (file)
--- 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);
 }