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Commit c97cb9cc authored by Davidlohr Bueso's avatar Davidlohr Bueso Committed by Linus Torvalds
Browse files

ipc,shm: make shmctl_nolock lockless 



While the INFO cmd doesn't take the ipc lock, the STAT commands do acquire
it unnecessarily.  We can do the permissions and security checks only
holding the rcu lock.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: default avatarDavidlohr Bueso <davidlohr.bueso@hp.com>
Tested-by: default avatarSedat Dilek <sedat.dilek@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 68eccc1d

ipc/shm.c

+12 −7
Original line number Diff line number Diff line
@@ -882,27 +882,31 @@ static int shmctl_nolock(struct ipc_namespace *ns, int shmid, 
		struct shmid64_ds tbuf;

		int result;



		rcu_read_lock();

		if (cmd == SHM_STAT) {

			shp = shm_lock(ns, shmid);

			shp = shm_obtain_object(ns, shmid);

			if (IS_ERR(shp)) {

				err = PTR_ERR(shp);

				goto out;

				goto out_unlock;

			}

			result = shp->shm_perm.id;

		} else {

			shp = shm_lock_check(ns, shmid);

			shp = shm_obtain_object_check(ns, shmid);

			if (IS_ERR(shp)) {

				err = PTR_ERR(shp);

				goto out;

				goto out_unlock;

			}

			result = 0;

		}



		err = -EACCES;

		if (ipcperms(ns, &shp->shm_perm, S_IRUGO))

			goto out_unlock;



		err = security_shm_shmctl(shp, cmd);

		if (err)

			goto out_unlock;



		memset(&tbuf, 0, sizeof(tbuf));

		kernel_to_ipc64_perm(&shp->shm_perm, &tbuf.shm_perm);

		tbuf.shm_segsz	= shp->shm_segsz;
@@ -912,7 +916,8 @@ static int shmctl_nolock(struct ipc_namespace *ns, int shmid, 
		tbuf.shm_cpid	= shp->shm_cprid;

		tbuf.shm_lpid	= shp->shm_lprid;

		tbuf.shm_nattch	= shp->shm_nattch;

		shm_unlock(shp);

		rcu_read_unlock();



		if (copy_shmid_to_user(buf, &tbuf, version))

			err = -EFAULT;

		else
@@ -924,7 +929,7 @@ static int shmctl_nolock(struct ipc_namespace *ns, int shmid, 
	}



out_unlock:

	shm_unlock(shp);

	rcu_read_unlock();

out:

	return err;

}