From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Lin Ma <linma@zju.edu.cn>,
        Jakub Kicinski <kuba@kernel.org>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 4.9 185/207] NFC: reorganize the functions in nci_request
Date:   Wed, 24 Nov 2021 12:57:36 +0100
Message-Id: <20211124115709.958456628@linuxfoundation.org>
In-Reply-To: <20211124115703.941380739@linuxfoundation.org>
References: <20211124115703.941380739@linuxfoundation.org>
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From: Lin Ma <linma@zju.edu.cn>

[ Upstream commit 86cdf8e38792545161dbe3350a7eced558ba4d15 ]

There is a possible data race as shown below:

thread-A in nci_request()       | thread-B in nci_close_device()
                                | mutex_lock(&ndev->req_lock);
test_bit(NCI_UP, &ndev->flags); |
...                             | test_and_clear_bit(NCI_UP, &ndev->flags)
mutex_lock(&ndev->req_lock);    |
                                |

This race will allow __nci_request() to be awaked while the device is
getting removed.

Similar to commit e2cb6b891ad2 ("bluetooth: eliminate the potential race
condition when removing the HCI controller"). this patch alters the
function sequence in nci_request() to prevent the data races between the
nci_close_device().

Signed-off-by: Lin Ma <linma@zju.edu.cn>
Fixes: 6a2968aaf50c ("NFC: basic NCI protocol implementation")
Link: https://lore.kernel.org/r/20211115145600.8320-1-linma@zju.edu.cn
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/nfc/nci/core.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/net/nfc/nci/core.c b/net/nfc/nci/core.c
index bff6ba84d3979..19518a231e571 100644
--- a/net/nfc/nci/core.c
+++ b/net/nfc/nci/core.c
@@ -157,12 +157,15 @@ inline int nci_request(struct nci_dev *ndev,
 {
 	int rc;
 
-	if (!test_bit(NCI_UP, &ndev->flags))
-		return -ENETDOWN;
-
 	/* Serialize all requests */
 	mutex_lock(&ndev->req_lock);
-	rc = __nci_request(ndev, req, opt, timeout);
+	/* check the state after obtaing the lock against any races
+	 * from nci_close_device when the device gets removed.
+	 */
+	if (test_bit(NCI_UP, &ndev->flags))
+		rc = __nci_request(ndev, req, opt, timeout);
+	else
+		rc = -ENETDOWN;
 	mutex_unlock(&ndev->req_lock);
 
 	return rc;
-- 
2.33.0