From c97cb9ccab8c85428ec21eff690642ad2ce1fa8a Mon Sep 17 00:00:00 2001
From: Davidlohr Bueso <davidlohr.bueso@hp.com>
Date: Wed, 11 Sep 2013 14:26:20 -0700
Subject: [PATCH] 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: 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
ipc/shm.c | 19 ++++++++++++-------
1 file changed, 12 insertions(+), 7 deletions(-)
diff --git a/ipc/shm.c b/ipc/shm.c
index 3e123987f054b..a493639550d93 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -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;
@@ -912,8 +916,9 @@ 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);
- if(copy_shmid_to_user (buf, &tbuf, version))
+ rcu_read_unlock();
+
+ if (copy_shmid_to_user(buf, &tbuf, version))
err = -EFAULT;
else
err = result;
@@ -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;
}
--
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