ipc,shm: introduce shmctl_nolock
Davidlohr Bueso [Wed, 11 Sep 2013 21:26:18 +0000 (14:26 -0700)]
commit 68eccc1dc345539d589ae78ee43b835c1a06a134 upstream.

Similar to semctl and msgctl, when calling msgctl, the *_INFO and *_STAT
commands can be performed without acquiring the ipc object.

Add a shmctl_nolock() function and move the logic of *_INFO and *_STAT out
of msgctl().  Since we are just moving functionality, this change still
takes the lock and it will be properly lockless in the next patch.

Signed-off-by: Davidlohr Bueso <davidlohr.bueso@hp.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

ipc/shm.c

index 9020ac8..ac118be 100644 (file)
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -820,29 +820,24 @@ out_up:
        return err;
 }
 
-SYSCALL_DEFINE3(shmctl, int, shmid, int, cmd, struct shmid_ds __user *, buf)
+static int shmctl_nolock(struct ipc_namespace *ns, int shmid,
+                        int cmd, int version, void __user *buf)
 {
+       int err;
        struct shmid_kernel *shp;
-       int err, version;
-       struct ipc_namespace *ns;
 
-       if (cmd < 0 || shmid < 0) {
-               err = -EINVAL;
-               goto out;
+       /* preliminary security checks for *_INFO */
+       if (cmd == IPC_INFO || cmd == SHM_INFO) {
+               err = security_shm_shmctl(NULL, cmd);
+               if (err)
+                       return err;
        }
 
-       version = ipc_parse_version(&cmd);
-       ns = current->nsproxy->ipc_ns;
-
-       switch (cmd) { /* replace with proc interface ? */
+       switch (cmd) {
        case IPC_INFO:
        {
                struct shminfo64 shminfo;
 
-               err = security_shm_shmctl(NULL, cmd);
-               if (err)
-                       return err;
-
                memset(&shminfo, 0, sizeof(shminfo));
                shminfo.shmmni = shminfo.shmseg = ns->shm_ctlmni;
                shminfo.shmmax = ns->shm_ctlmax;
@@ -864,10 +859,6 @@ SYSCALL_DEFINE3(shmctl, int, shmid, int, cmd, struct shmid_ds __user *, buf)
        {
                struct shm_info shm_info;
 
-               err = security_shm_shmctl(NULL, cmd);
-               if (err)
-                       return err;
-
                memset(&shm_info, 0, sizeof(shm_info));
                down_read(&shm_ids(ns).rw_mutex);
                shm_info.used_ids = shm_ids(ns).in_use;
@@ -928,6 +919,36 @@ SYSCALL_DEFINE3(shmctl, int, shmid, int, cmd, struct shmid_ds __user *, buf)
                        err = result;
                goto out;
        }
+       default:
+               return -EINVAL;
+       }
+
+out_unlock:
+       shm_unlock(shp);
+out:
+       return err;
+}
+
+SYSCALL_DEFINE3(shmctl, int, shmid, int, cmd, struct shmid_ds __user *, buf)
+{
+       struct shmid_kernel *shp;
+       int err, version;
+       struct ipc_namespace *ns;
+
+       if (cmd < 0 || shmid < 0) {
+               err = -EINVAL;
+               goto out;
+       }
+
+       version = ipc_parse_version(&cmd);
+       ns = current->nsproxy->ipc_ns;
+
+       switch (cmd) {
+       case IPC_INFO:
+       case SHM_INFO:
+       case SHM_STAT:
+       case IPC_STAT:
+               return shmctl_nolock(ns, shmid, cmd, version, buf);
        case SHM_LOCK:
        case SHM_UNLOCK:
        {