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From:   Deepak Kumar Singh <quic_deesin@quicinc.com>
To:     <bjorn.andersson@linaro.org>, <swboyd@chromium.org>,
        <quic_clew@quicinc.com>, <mathieu.poirier@linaro.org>
CC:     <linux-kernel@vger.kernel.org>, <linux-arm-msm@vger.kernel.org>,
        <linux-remoteproc@vger.kernel.org>,
        Deepak Kumar Singh <quic_deesin@quicinc.com>,
        Ohad Ben-Cohen <ohad@wizery.com>
Subject: [PATCH V1 2/3] rpmsg: glink: Add lock to avoid race when rpmsg device is released
Date:   Thu, 27 Jan 2022 00:34:45 +0530
Message-ID: <1643223886-28170-3-git-send-email-quic_deesin@quicinc.com>
In-Reply-To: <1643223886-28170-1-git-send-email-quic_deesin@quicinc.com>
References: <1643223886-28170-1-git-send-email-quic_deesin@quicinc.com>
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When remote host goes down glink char device channel is freed,
At the same time user space apps can still try to open rpmsg_char
device which will result in calling rpmsg_create_ept. This may cause
reference to already freed context of glink chardev channel.

Use per ept lock to avoid race between rpmsg_destroy_ept and
rpmsg_destory_ept.
---
 drivers/rpmsg/rpmsg_char.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/rpmsg/rpmsg_char.c b/drivers/rpmsg/rpmsg_char.c
index 72ee101..2108ef8 100644
--- a/drivers/rpmsg/rpmsg_char.c
+++ b/drivers/rpmsg/rpmsg_char.c
@@ -85,6 +85,7 @@ static int rpmsg_eptdev_destroy(struct device *dev, void *data)
 	struct rpmsg_eptdev *eptdev = dev_to_eptdev(dev);
 
 	mutex_lock(&eptdev->ept_lock);
+	eptdev->rpdev = NULL;
 	if (eptdev->ept) {
 		rpmsg_destroy_ept(eptdev->ept);
 		eptdev->ept = NULL;
@@ -145,15 +146,24 @@ static int rpmsg_eptdev_open(struct inode *inode, struct file *filp)
 
 	get_device(dev);
 
+	mutex_lock(&eptdev->ept_lock);
+	if (!eptdev->rpdev) {
+		put_device(dev);
+		mutex_unlock(&eptdev->ept_lock);
+		return -ENETRESET;
+	}
+
 	ept = rpmsg_create_ept(rpdev, rpmsg_ept_cb, eptdev, eptdev->chinfo);
 	if (!ept) {
 		dev_err(dev, "failed to open %s\n", eptdev->chinfo.name);
+		mutex_unlock(&eptdev->ept_lock);
 		put_device(dev);
 		return -EINVAL;
 	}
 
 	ept->sig_cb = rpmsg_sigs_cb;
 	eptdev->ept = ept;
+	mutex_unlock(&eptdev->ept_lock);
 	filp->private_data = eptdev;
 
 	return 0;
@@ -285,7 +295,9 @@ static __poll_t rpmsg_eptdev_poll(struct file *filp, poll_table *wait)
 	if (eptdev->sig_pending)
 		mask |= EPOLLPRI;
 
+	mutex_lock(&eptdev->ept_lock);
 	mask |= rpmsg_poll(eptdev->ept, filp, wait);
+	mutex_unlock(&eptdev->ept_lock);
 
 	return mask;
 }
-- 
2.7.4