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Subject[PATCH 2.6.24-mm1 3/8] (resend) IPC/message queues: introduce msgctl_down
From: Pierre Peiffer <pierre.peiffer@bull.net>

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>
---
ipc/msg.c | 162 ++++++++++++++++++++++++++++++++++----------------------------
1 file changed, 89 insertions(+), 73 deletions(-)
Index: b/ipc/msg.c
===================================================================
--- a/ipc/msg.c
+++ b/ipc/msg.c
@@ -436,10 +436,95 @@ copy_msqid_from_user(struct msq_setbuf *
}
}

-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, in
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;
--
Pierre Peiffer


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