linux-kernel - [PATCH 2/3] nfc: trf7970a: Prevent repeated polling from crashing the kernel

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Message-Id: <1482250250-4192-4-git-send-email-glansberry@gmail.com>
Date:   Tue, 20 Dec 2016 11:10:47 -0500
From:   Geoff Lansberry <geoff@...ee.com>
To:     linux-wireless@...r.kernel.org
Cc:     lauro.venancio@...nbossa.org, aloisio.almeida@...nbossa.org,
        sameo@...ux.intel.com, robh+dt@...nel.org, mark.rutland@....com,
        netdev@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, mgreer@...malcreek.com,
        justin@...ee.com, Jaret Cantu <jaret.cantu@...esys.com>,
        Geoff Lansberry <geoff@...ee.com>
Subject: [PATCH 2/3] nfc: trf7970a: Prevent repeated polling from crashing the kernel

From: Jaret Cantu <jaret.cantu@...esys.com>

Repeated polling attempts cause a NULL dereference error to occur.
This is because the state of the trf7970a is currently reading but
another request has been made to send a command before it has finished.

The solution is to properly kill the waiting reading (workqueue)
before failing on the send.
---
 drivers/nfc/trf7970a.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/nfc/trf7970a.c b/drivers/nfc/trf7970a.c
index 94c31f8..e9e93ea 100644
--- a/drivers/nfc/trf7970a.c
+++ b/drivers/nfc/trf7970a.c
@@ -1496,6 +1496,10 @@ static int trf7970a_send_cmd(struct nfc_digital_dev *ddev,
 			(trf->state != TRF7970A_ST_IDLE_RX_BLOCKED)) {
 		dev_err(trf->dev, "%s - Bogus state: %d\n", __func__,
 				trf->state);
+		if (trf->state == TRF7970A_ST_WAIT_FOR_RX_DATA ||
+		    trf->state == TRF7970A_ST_WAIT_FOR_RX_DATA_CONT)
+			trf->ignore_timeout =
+				!cancel_delayed_work(&trf->timeout_work);
 		ret = -EIO;
 		goto out_err;
 	}
-- 
Signed-off-by: Geoff Lansberry <geoff@...ee.com>