ipc,shm: shorten critical region for shmat

Similar to other system calls, acquire the kern_ipc_perm lock after doing
the initial permission and security checks.

[sasha.levin@oracle.com: dont leave do_shmat with rcu lock held]
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: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 10 insertions, 4 deletions

diff --git a/ipc/shm.c b/ipc/shm.c
index 115dccebc63e..28d19f4ece4b 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -19,6 +19,9 @@
  * namespaces support
  * OpenVZ, SWsoft Inc.
  * Pavel Emelianov <xemul@openvz.org>
+ *
+ * Better ipc lock (kern_ipc_perm.lock) handling
+ * Davidlohr Bueso <davidlohr.bueso@hp.com>, June 2013.
  */
 
 #include <linux/slab.h>
@@ -1086,10 +1089,11 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr,
          * additional creator id...
          */
         ns = current->nsproxy->ipc_ns;
-        shp = shm_lock_check(ns, shmid);
+        rcu_read_lock();
+        shp = shm_obtain_object_check(ns, shmid);
         if (IS_ERR(shp)) {
                 err = PTR_ERR(shp);
-                goto out;
+                goto out_unlock;
         }
 
         err = -EACCES;
@@ -1100,11 +1104,13 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr,
         if (err)
                 goto out_unlock;
 
+        ipc_lock_object(&shp->shm_perm);
         path = shp->shm_file->f_path;
         path_get(&path);
         shp->shm_nattch++;
         size = i_size_read(path.dentry->d_inode);
-        shm_unlock(shp);
+        ipc_unlock_object(&shp->shm_perm);
+        rcu_read_unlock();
 
         err = -ENOMEM;
         sfd = kzalloc(sizeof(*sfd), GFP_KERNEL);
@@ -1175,7 +1181,7 @@ out_nattch:
         return err;
 
 out_unlock:
-        shm_unlock(shp);
+        rcu_read_unlock();
 out:
         return err;
 }