[ 39/50] ipc,shm: shorten critical region for shmat

[Greg Kroah-Hartman]

3.11-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Davidlohr Bueso <davidlohr.bueso@xxxxxx>

commit c2c737a0461e61a34676bd0bd1bc1a70a1b4e396 upstream.

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

[sasha.levin@xxxxxxxxxx: dont leave do_shmat with rcu lock held]
Signed-off-by: Davidlohr Bueso <davidlohr.bueso@xxxxxx>
Tested-by: Sedat Dilek <sedat.dilek@xxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sasha.levin@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Mike Galbraith <efault@xxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 ipc/shm.c |   14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -19,6 +19,9 @@
  * namespaces support
  * OpenVZ, SWsoft Inc.
  * Pavel Emelianov <xemul@xxxxxxxxxx>
+ *
+ * Better ipc lock (kern_ipc_perm.lock) handling
+ * Davidlohr Bueso <davidlohr.bueso@xxxxxx>, June 2013.
  */
 
 #include <linux/slab.h>
@@ -1093,10 +1096,11 @@ long do_shmat(int shmid, char __user *sh
 	 * 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;
@@ -1107,11 +1111,13 @@ long do_shmat(int shmid, char __user *sh
 	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);
@@ -1182,7 +1188,7 @@ out_nattch:
 	return err;
 
 out_unlock:
-	shm_unlock(shp);
+	rcu_read_unlock();
 out:
 	return err;
 }


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