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From: Davidlohr Bueso <dave@stgolabs.net>
To: akpm@linux-foundation.org
Cc: manfred@colorfullife.com, bigeasy@linutronix.de,
	peterz@infradead.org, tglx@linutronix.de, dave@stgolabs.net,
	linux-kernel@vger.kernel.org, Davidlohr Bueso <dbueso@suse.de>
Subject: [PATCH 4/5] ipc/msg: Lockless security checks for msgsnd
Date: Thu, 28 Jul 2016 16:33:38 -0700	[thread overview]
Message-ID: <1469748819-19484-5-git-send-email-dave@stgolabs.net> (raw)
In-Reply-To: <1469748819-19484-1-git-send-email-dave@stgolabs.net>

Just as with msgrcv (along with the rest of sysvipc since a few
years ago), perform the security checks without holding the ipc
object lock. This also reduces the hogging of the lock for the
entire duration of a sender, as we drop the lock upon every
iteration -- and this is exactly why we also check for racing
with RMID in the first place.

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
---
 ipc/msg.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/ipc/msg.c b/ipc/msg.c
index 5181259e2ff0..fe793304dddb 100644
--- a/ipc/msg.c
+++ b/ipc/msg.c
@@ -623,14 +623,14 @@ long do_msgsnd(int msqid, long mtype, void __user *mtext,
 		goto out_unlock1;
 	}
 
-	ipc_lock_object(&msq->q_perm);
-
 	for (;;) {
 		struct msg_sender s;
 
 		err = -EACCES;
 		if (ipcperms(ns, &msq->q_perm, S_IWUGO))
-			goto out_unlock0;
+			goto out_unlock1;
+
+		ipc_lock_object(&msq->q_perm);
 
 		/* raced with RMID? */
 		if (!ipc_valid_object(&msq->q_perm)) {
@@ -681,6 +681,7 @@ long do_msgsnd(int msqid, long mtype, void __user *mtext,
 			goto out_unlock0;
 		}
 
+		ipc_unlock_object(&msq->q_perm);
 	}
 	msq->q_lspid = task_tgid_vnr(current);
 	msq->q_stime = get_seconds();
-- 
2.6.6

  parent reply	other threads:[~2016-07-28 23:34 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-07-28 23:33 [PATCH 0/5] ipc/msg: Sender/receiver optimizations Davidlohr Bueso
2016-07-28 23:33 ` [PATCH 1/5] ipc/msg: Implement lockless pipelined wakeups Davidlohr Bueso
2016-07-28 23:33 ` [PATCH 2/5] ipc/msg: Batch queue sender wakeups Davidlohr Bueso
2016-07-28 23:33 ` [PATCH 3/5] ipc/msg: Make ss_wakeup() kill arg boolean Davidlohr Bueso
2016-07-28 23:33 ` Davidlohr Bueso [this message]
2016-07-28 23:33 ` [PATCH 5/5] ipc/msg: Avoid waking sender upon full queue Davidlohr Bueso
2016-08-04 16:44 ` [PATCH 0/5] ipc/msg: Sender/receiver optimizations Peter Zijlstra
2016-08-09 12:44   ` Peter Zijlstra
2016-08-09 18:31     ` Andrew Morton
2016-09-18  5:10 [PATCH 4/5] ipc/msg: Lockless security checks for msgsnd Manfred Spraul
2016-09-21 22:21 ` Davidlohr Bueso
2016-09-22 19:42   ` Manfred Spraul

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