ipc,shm: introduce shmctl_nolock

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>

1 files changed, 39 insertions, 18 deletions

diff --git a/ipc/shm.c b/ipc/shm.c
index 22cffd78dbb1..3e123987f054 100644
--- 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:
         {