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

From: Colin King
Date: Fri Apr 06 2018 - 12:05:51 EST

From: Colin Ian King <colin.king@xxxxxxxxxxxxx>

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@xxxxxxxxxxxxx>
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;