linux-kernel - [PATCH 08/11] ipc,shm: shorten critical region for shmat

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Date:	Tue, 18 Jun 2013 18:18:33 -0700
From:	Davidlohr Bueso <davidlohr.bueso@...com>
To:	akpm@...ux-foundation.org, riel@...hat.com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc:	Davidlohr Bueso <davidlohr.bueso@...com>
Subject: [PATCH 08/11] 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.

Signed-off-by: Davidlohr Bueso <davidlohr.bueso@...com>
---
 ipc/shm.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/ipc/shm.c b/ipc/shm.c
index d1b3ebf..2fe6170 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -19,6 +19,9 @@
  * namespaces support
  * OpenVZ, SWsoft Inc.
  * Pavel Emelianov <xemul@...nvz.org>
+ *
+ * Better ipc lock (kern_ipc_perm.lock) handling
+ * Davidlohr Bueso <davidlohr.bueso@...com>, June 2013.
  */
 
 #include <linux/slab.h>
@@ -1086,7 +1089,8 @@ 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;
@@ -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;
 }
-- 
1.7.11.7

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