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

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Message-ID: <20180406160711.GA14097@ziepe.ca>
Date:   Fri, 6 Apr 2018 10:07:11 -0600
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Colin King <colin.king@...onical.com>
Cc:     Peter Huewe <peterhuewe@....de>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-integrity@...r.kernel.org, kernel-janitors@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tpm: st33zp24: check if chip is null before dereferencing

On Fri, Apr 06, 2018 at 05:05:41PM +0100, Colin King wrote:
> 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
> +++ 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;

Chip can't be NULL here, so I would prefer to see the NULL test
deleted.

Thanks,
Jason