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Subject[ 39/50] ipc,shm: shorten critical region for shmat
Date
3.11-stable review patch.  If anyone has any objections, please let me know.

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

From: Davidlohr Bueso <davidlohr.bueso@hp.com>

commit c2c737a0461e61a34676bd0bd1bc1a70a1b4e396 upstream.

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>
Cc: Mike Galbraith <efault@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
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@openvz.org>
+ *
+ * Better ipc lock (kern_ipc_perm.lock) handling
+ * Davidlohr Bueso <davidlohr.bueso@hp.com>, 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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