linux-kernel - [PATCH] xen: xenbus: Fix a possible data race in xs_request

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Date:   Tue,  8 May 2018 11:34:29 +0800
From:   Jia-Ju Bai <baijiaju1990@...il.com>
To:     boris.ostrovsky@...cle.com, jgross@...e.com,
        simon@...isiblethingslab.com, joao.m.martins@...cle.com
Cc:     xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
        Jia-Ju Bai <baijiaju1990@...il.com>
Subject: [PATCH] xen: xenbus: Fix a possible data race in xs_request_enter

The read operation to "req->type" is protected by
the lock on line 128, but the write operation to
this data on line 118 is not protected by the lock.
Thus, there may exist a data race for "req->type".

To fix this data race, the write operation to "req->type" 
should be also protected by the lock.

Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>
---
 drivers/xen/xenbus/xenbus_xs.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/xen/xenbus/xenbus_xs.c b/drivers/xen/xenbus/xenbus_xs.c
index 49a3874ae6bb..274cdfee08b1 100644
--- a/drivers/xen/xenbus/xenbus_xs.c
+++ b/drivers/xen/xenbus/xenbus_xs.c
@@ -115,10 +115,10 @@ static uint32_t xs_request_enter(struct xb_req_data *req)
 {
 	uint32_t rq_id;
 
-	req->type = req->msg.type;
-
 	spin_lock(&xs_state_lock);
 
+	req->type = req->msg.type;
+
 	while (!xs_state_users && xs_suspend_active) {
 		spin_unlock(&xs_state_lock);
 		wait_event(xs_state_enter_wq, xs_suspend_active == 0);
-- 
2.17.0