linux-kernel - [PATCH] staging: comedi: Fix comedi_device refcnt leak in comedi

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Message-Id: <1587361459-83622-1-git-send-email-xiyuyang19@fudan.edu.cn>
Date:   Mon, 20 Apr 2020 13:44:16 +0800
From:   Xiyu Yang <xiyuyang19@...an.edu.cn>
To:     Ian Abbott <abbotti@....co.uk>,
        H Hartley Sweeten <hsweeten@...ionengravers.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Xiyu Yang <xiyuyang19@...an.edu.cn>,
        Xin Tan <tanxin.ctf@...il.com>, devel@...verdev.osuosl.org,
        linux-kernel@...r.kernel.org
Cc:     yuanxzhang@...an.edu.cn, kjlu@....edu
Subject: [PATCH] staging: comedi: Fix comedi_device refcnt leak in comedi_open

comedi_open() invokes comedi_dev_get_from_minor(), which returns a
reference of the COMEDI device to "dev" with increased refcount.

When comedi_open() returns, "dev" becomes invalid, so the refcount
should be decreased to keep refcount balanced.

The reference counting issue happens in one exception handling path of
comedi_open(). When "cfp" allocation is failed, the refcnt increased by
comedi_dev_get_from_minor() is not decreased, causing a refcnt leak.

Fix this issue by calling comedi_dev_put() on this error path when "cfp"
allocation is failed.

Fixes: 20f083c07565 ("staging: comedi: prepare support for per-file read
and write subdevices")
Signed-off-by: Xiyu Yang <xiyuyang19@...an.edu.cn>
Signed-off-by: Xin Tan <tanxin.ctf@...il.com>
---
 drivers/staging/comedi/comedi_fops.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c
index 08d1bbbebf2d..e84b4fb493d6 100644
--- a/drivers/staging/comedi/comedi_fops.c
+++ b/drivers/staging/comedi/comedi_fops.c
@@ -2725,8 +2725,10 @@ static int comedi_open(struct inode *inode, struct file *file)
 	}
 
 	cfp = kzalloc(sizeof(*cfp), GFP_KERNEL);
-	if (!cfp)
+	if (!cfp) {
+		comedi_dev_put(dev);
 		return -ENOMEM;
+	}
 
 	cfp->dev = dev;
 
-- 
2.7.4