IPC/message queues: introduce msgctl_down

Currently, sys_msgctl is not easy to read.

This patch tries to improve that by introducing the msgctl_down function to
handle all commands requiring the rwmutex to be taken in write mode (ie
IPC_SET and IPC_RMID for now).  It is the equivalent function of semctl_down
for message queues.

This greatly changes the readability of sys_msgctl and also harmonizes the way
these commands are handled among all IPCs.

Signed-off-by: Pierre Peiffer <pierre.peiffer@bull.net>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Cc: Nadia Derbey <Nadia.Derbey@bull.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/ipc/msg.c b/ipc/msg.c
index 7d9b069..9d868b3 100644 (file)
--- a/ipc/msg.c
+++ b/ipc/msg.c
@@ -436,10 +436,95 @@ copy_msqid_from_user(struct msq_setbuf *out, void __user *buf, int version)
        }
 }
 
-asmlinkage long sys_msgctl(int msqid, int cmd, struct msqid_ds __user *buf)
+/*
+ * This function handles some msgctl commands which require the rw_mutex
+ * to be held in write mode.
+ * NOTE: no locks must be held, the rw_mutex is taken inside this function.
+ */
+static int msgctl_down(struct ipc_namespace *ns, int msqid, int cmd,
+                      struct msqid_ds __user *buf, int version)
 {
        struct kern_ipc_perm *ipcp;
-       struct msq_setbuf uninitialized_var(setbuf);
+       struct msq_setbuf setbuf;
+       struct msg_queue *msq;
+       int err;
+
+       if (cmd == IPC_SET) {
+               if (copy_msqid_from_user(&setbuf, buf, version))
+                       return -EFAULT;
+       }
+
+       down_write(&msg_ids(ns).rw_mutex);
+       msq = msg_lock_check_down(ns, msqid);
+       if (IS_ERR(msq)) {
+               err = PTR_ERR(msq);
+               goto out_up;
+       }
+
+       ipcp = &msq->q_perm;
+
+       err = audit_ipc_obj(ipcp);
+       if (err)
+               goto out_unlock;
+
+       if (cmd == IPC_SET) {
+               err = audit_ipc_set_perm(setbuf.qbytes, setbuf.uid, setbuf.gid,
+                                        setbuf.mode);
+               if (err)
+                       goto out_unlock;
+       }
+
+       if (current->euid != ipcp->cuid &&
+           current->euid != ipcp->uid &&
+           !capable(CAP_SYS_ADMIN)) {
+               /* We _could_ check for CAP_CHOWN above, but we don't */
+               err = -EPERM;
+               goto out_unlock;
+       }
+
+       err = security_msg_queue_msgctl(msq, cmd);
+       if (err)
+               goto out_unlock;
+
+       switch (cmd) {
+       case IPC_RMID:
+               freeque(ns, ipcp);
+               goto out_up;
+       case IPC_SET:
+               if (setbuf.qbytes > ns->msg_ctlmnb &&
+                   !capable(CAP_SYS_RESOURCE)) {
+                       err = -EPERM;
+                       goto out_unlock;
+               }
+
+               msq->q_qbytes = setbuf.qbytes;
+
+               ipcp->uid = setbuf.uid;
+               ipcp->gid = setbuf.gid;
+               ipcp->mode = (ipcp->mode & ~S_IRWXUGO) |
+                            (S_IRWXUGO & setbuf.mode);
+               msq->q_ctime = get_seconds();
+               /* sleeping receivers might be excluded by
+                * stricter permissions.
+                */
+               expunge_all(msq, -EAGAIN);
+               /* sleeping senders might be able to send
+                * due to a larger queue size.
+                */
+               ss_wakeup(&msq->q_senders, 0);
+               break;
+       default:
+               err = -EINVAL;
+       }
+out_unlock:
+       msg_unlock(msq);
+out_up:
+       up_write(&msg_ids(ns).rw_mutex);
+       return err;
+}
+
+asmlinkage long sys_msgctl(int msqid, int cmd, struct msqid_ds __user *buf)
+{
        struct msg_queue *msq;
        int err, version;
        struct ipc_namespace *ns;
@@ -535,82 +620,13 @@ asmlinkage long sys_msgctl(int msqid, int cmd, struct msqid_ds __user *buf)
                return success_return;
        }
        case IPC_SET:
-               if (!buf)
-                       return -EFAULT;
-               if (copy_msqid_from_user(&setbuf, buf, version))
-                       return -EFAULT;
-               break;
        case IPC_RMID:
-               break;
+               err = msgctl_down(ns, msqid, cmd, buf, version);
+               return err;
        default:
                return  -EINVAL;
        }
 
-       down_write(&msg_ids(ns).rw_mutex);
-       msq = msg_lock_check_down(ns, msqid);
-       if (IS_ERR(msq)) {
-               err = PTR_ERR(msq);
-               goto out_up;
-       }
-
-       ipcp = &msq->q_perm;
-
-       err = audit_ipc_obj(ipcp);
-       if (err)
-               goto out_unlock_up;
-       if (cmd == IPC_SET) {
-               err = audit_ipc_set_perm(setbuf.qbytes, setbuf.uid, setbuf.gid,
-                                        setbuf.mode);
-               if (err)
-                       goto out_unlock_up;
-       }
-
-       err = -EPERM;
-       if (current->euid != ipcp->cuid &&
-           current->euid != ipcp->uid && !capable(CAP_SYS_ADMIN))
-               /* We _could_ check for CAP_CHOWN above, but we don't */
-               goto out_unlock_up;
-
-       err = security_msg_queue_msgctl(msq, cmd);
-       if (err)
-               goto out_unlock_up;
-
-       switch (cmd) {
-       case IPC_SET:
-       {
-               err = -EPERM;
-               if (setbuf.qbytes > ns->msg_ctlmnb && !capable(CAP_SYS_RESOURCE))
-                       goto out_unlock_up;
-
-               msq->q_qbytes = setbuf.qbytes;
-
-               ipcp->uid = setbuf.uid;
-               ipcp->gid = setbuf.gid;
-               ipcp->mode = (ipcp->mode & ~S_IRWXUGO) |
-                            (S_IRWXUGO & setbuf.mode);
-               msq->q_ctime = get_seconds();
-               /* sleeping receivers might be excluded by
-                * stricter permissions.
-                */
-               expunge_all(msq, -EAGAIN);
-               /* sleeping senders might be able to send
-                * due to a larger queue size.
-                */
-               ss_wakeup(&msq->q_senders, 0);
-               msg_unlock(msq);
-               break;
-       }
-       case IPC_RMID:
-               freeque(ns, &msq->q_perm);
-               break;
-       }
-       err = 0;
-out_up:
-       up_write(&msg_ids(ns).rw_mutex);
-       return err;
-out_unlock_up:
-       msg_unlock(msq);
-       goto out_up;
 out_unlock:
        msg_unlock(msq);
        return err;