IPC/shared memory: introduce shmctl_down

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>

1 files changed, 72 insertions, 88 deletions

diff --git a/ipc/shm.c b/ipc/shm.c
index 3e4aff982546..65a44bcc4ac2 100644
--- 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: