linux-kernel - [PATCH] tpm: st33zp24: check if chip is null before dereferencing

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Message-Id: <20180406160541.8188-1-colin.king@canonical.com>
Date:   Fri,  6 Apr 2018 17:05:41 +0100
From:   Colin King <colin.king@...onical.com>
To:     Peter Huewe <peterhuewe@....de>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Jason Gunthorpe <jgg@...pe.ca>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-integrity@...r.kernel.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] tpm: st33zp24: check if chip is null before dereferencing

From: Colin Ian King <colin.king@...onical.com>

Currently chip is being dereferenced by the call to dev_get_drvdata
before it is being null checked, hence we have a potential null
pointer dereference bug. Fix this by only dereferencing it after the
null check.

Detected by CoverityScan, CID#1357806 ("Dereference before null check")

Fixes: 9e0d39d8a6a0 ("tpm: Remove useless priv field in struct tpm_vendor_specific")
Signed-off-by: Colin Ian King <colin.king@...onical.com>
---
 drivers/char/tpm/st33zp24/st33zp24.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/char/tpm/st33zp24/st33zp24.c b/drivers/char/tpm/st33zp24/st33zp24.c
index f95b9c75175b..476865d66a0e 100644
--- a/drivers/char/tpm/st33zp24/st33zp24.c
+++ b/drivers/char/tpm/st33zp24/st33zp24.c
@@ -367,7 +367,7 @@ static irqreturn_t tpm_ioserirq_handler(int irq, void *dev_id)
 static int st33zp24_send(struct tpm_chip *chip, unsigned char *buf,
 			 size_t len)
 {
-	struct st33zp24_dev *tpm_dev = dev_get_drvdata(&chip->dev);
+	struct st33zp24_dev *tpm_dev;
 	u32 status, i, size, ordinal;
 	int burstcnt = 0;
 	int ret;
@@ -378,6 +378,7 @@ static int st33zp24_send(struct tpm_chip *chip, unsigned char *buf,
 	if (len < TPM_HEADER_SIZE)
 		return -EBUSY;
 
+	tpm_dev = dev_get_drvdata(&chip->dev);
 	ret = request_locality(chip);
 	if (ret < 0)
 		return ret;
-- 
2.15.1