IPC/shared memory: introduce shmctl_down
Pierre Peiffer [Tue, 29 Apr 2008 08:00:47 +0000 (01:00 -0700)]
Currently, the way the different commands are handled in sys_shmctl introduces
some duplicated code.

This patch introduces the shmctl_down function to handle all the 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 shared memory.

This removes some duplicated code for handling these both commands and
harmonizes the way they 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>

ipc/shm.c

index 3e4aff9..65a44bc 100644 (file)
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -616,10 +616,78 @@ static void shm_get_stat(struct ipc_namespace *ns, unsigned long *rss,
        }
 }
 
-asmlinkage long sys_shmctl (int shmid, int cmd, struct shmid_ds __user *buf)
+/*
+ * This function handles some shmctl 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 shmctl_down(struct ipc_namespace *ns, int shmid, int cmd,
+                      struct shmid_ds __user *buf, int version)
 {
+       struct kern_ipc_perm *ipcp;
        struct shm_setbuf setbuf;
        struct shmid_kernel *shp;
+       int err;
+
+       if (cmd == IPC_SET) {
+               if (copy_shmid_from_user(&setbuf, buf, version))
+                       return -EFAULT;
+       }
+
+       down_write(&shm_ids(ns).rw_mutex);
+       shp = shm_lock_check_down(ns, shmid);
+       if (IS_ERR(shp)) {
+               err = PTR_ERR(shp);
+               goto out_up;
+       }
+
+       ipcp = &shp->shm_perm;
+
+       err = audit_ipc_obj(ipcp);
+       if (err)
+               goto out_unlock;
+
+       if (cmd == IPC_SET) {
+               err = audit_ipc_set_perm(0, setbuf.uid,
+                                        setbuf.gid, setbuf.mode);
+               if (err)
+                       goto out_unlock;
+       }
+
+       if (current->euid != ipcp->uid &&
+           current->euid != ipcp->cuid &&
+           !capable(CAP_SYS_ADMIN)) {
+               err = -EPERM;
+               goto out_unlock;
+       }
+
+       err = security_shm_shmctl(shp, cmd);
+       if (err)
+               goto out_unlock;
+       switch (cmd) {
+       case IPC_RMID:
+               do_shm_rmid(ns, ipcp);
+               goto out_up;
+       case IPC_SET:
+               ipcp->uid = setbuf.uid;
+               ipcp->gid = setbuf.gid;
+               ipcp->mode = (ipcp->mode & ~S_IRWXUGO)
+                       | (setbuf.mode & S_IRWXUGO);
+               shp->shm_ctim = get_seconds();
+               break;
+       default:
+               err = -EINVAL;
+       }
+out_unlock:
+       shm_unlock(shp);
+out_up:
+       up_write(&shm_ids(ns).rw_mutex);
+       return err;
+}
+
+asmlinkage long sys_shmctl(int shmid, int cmd, struct shmid_ds __user *buf)
+{
+       struct shmid_kernel *shp;
        int err, version;
        struct ipc_namespace *ns;
 
@@ -775,97 +843,13 @@ asmlinkage long sys_shmctl (int shmid, int cmd, struct shmid_ds __user *buf)
                goto out;
        }
        case IPC_RMID:
-       {
-               /*
-                *      We cannot simply remove the file. The SVID states
-                *      that the block remains until the last person
-                *      detaches from it, then is deleted. A shmat() on
-                *      an RMID segment is legal in older Linux and if 
-                *      we change it apps break...
-                *
-                *      Instead we set a destroyed flag, and then blow
-                *      the name away when the usage hits zero.
-                */
-               down_write(&shm_ids(ns).rw_mutex);
-               shp = shm_lock_check_down(ns, shmid);
-               if (IS_ERR(shp)) {
-                       err = PTR_ERR(shp);
-                       goto out_up;
-               }
-
-               err = audit_ipc_obj(&(shp->shm_perm));
-               if (err)
-                       goto out_unlock_up;
-
-               if (current->euid != shp->shm_perm.uid &&
-                   current->euid != shp->shm_perm.cuid && 
-                   !capable(CAP_SYS_ADMIN)) {
-                       err=-EPERM;
-                       goto out_unlock_up;
-               }
-
-               err = security_shm_shmctl(shp, cmd);
-               if (err)
-                       goto out_unlock_up;
-
-               do_shm_rmid(ns, &shp->shm_perm);
-               up_write(&shm_ids(ns).rw_mutex);
-               goto out;
-       }
-
        case IPC_SET:
-       {
-               if (!buf) {
-                       err = -EFAULT;
-                       goto out;
-               }
-
-               if (copy_shmid_from_user (&setbuf, buf, version)) {
-                       err = -EFAULT;
-                       goto out;
-               }
-               down_write(&shm_ids(ns).rw_mutex);
-               shp = shm_lock_check_down(ns, shmid);
-               if (IS_ERR(shp)) {
-                       err = PTR_ERR(shp);
-                       goto out_up;
-               }
-               err = audit_ipc_obj(&(shp->shm_perm));
-               if (err)
-                       goto out_unlock_up;
-               err = audit_ipc_set_perm(0, setbuf.uid, setbuf.gid, setbuf.mode);
-               if (err)
-                       goto out_unlock_up;
-               err=-EPERM;
-               if (current->euid != shp->shm_perm.uid &&
-                   current->euid != shp->shm_perm.cuid && 
-                   !capable(CAP_SYS_ADMIN)) {
-                       goto out_unlock_up;
-               }
-
-               err = security_shm_shmctl(shp, cmd);
-               if (err)
-                       goto out_unlock_up;
-               
-               shp->shm_perm.uid = setbuf.uid;
-               shp->shm_perm.gid = setbuf.gid;
-               shp->shm_perm.mode = (shp->shm_perm.mode & ~S_IRWXUGO)
-                       | (setbuf.mode & S_IRWXUGO);
-               shp->shm_ctim = get_seconds();
-               break;
-       }
-
+               err = shmctl_down(ns, shmid, cmd, buf, version);
+               return err;
        default:
-               err = -EINVAL;
-               goto out;
+               return -EINVAL;
        }
 
-       err = 0;
-out_unlock_up:
-       shm_unlock(shp);
-out_up:
-       up_write(&shm_ids(ns).rw_mutex);
-       goto out;
 out_unlock:
        shm_unlock(shp);
 out: