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>

1 files changed, 89 insertions, 73 deletions

diff --git a/ipc/msg.c b/ipc/msg.c
index 7d9b0694c743..9d868b3d3329 100644
--- 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;