Re: [PATCH 2/2] tpm drivers: fix potential buffer overruns caused by bit glitches on the bus

[Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>]

On Fri, Feb 02, 2018 at 06:25:33PM +0100, James Bottomley wrote:
> From: Jeremy Boone <jeremy.boone@nccgroup.trust>
> 
> Discrete TPMs are often connected over slow serial buses which, on
> some platforms, can have glitches causing bit flips.  In all the
> driver _recv() functions, we need to use a u32 to unmarshal the
> response size, otherwise a bit flip of the 31st bit would cause the
> expected variable to go negative, which would then try to read a huge
> amount of data.  Also sanity check that the expected amount of data is
> large enough for the TPM header.
> 
> Signed-off-by: Jeremy Boone <jeremy.boone@nccgroup.trust>
> Cc: stable@vger.kernel.org
> Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
> ---
>  drivers/char/tpm/st33zp24/st33zp24.c | 4 ++--
>  drivers/char/tpm/tpm_i2c_infineon.c  | 5 +++--
>  drivers/char/tpm/tpm_i2c_nuvoton.c   | 5 +++--
>  drivers/char/tpm/tpm_tis_core.c      | 5 +++--
>  4 files changed, 11 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/char/tpm/st33zp24/st33zp24.c b/drivers/char/tpm/st33zp24/st33zp24.c
> index 4d1dc8b46877..f95b9c75175b 100644
> --- a/drivers/char/tpm/st33zp24/st33zp24.c
> +++ b/drivers/char/tpm/st33zp24/st33zp24.c
> @@ -457,7 +457,7 @@ static int st33zp24_recv(struct tpm_chip *chip, unsigned char *buf,
>  			    size_t count)
>  {
>  	int size = 0;
> -	int expected;
> +	u32 expected;
>  
>  	if (!chip)
>  		return -EBUSY;
> @@ -474,7 +474,7 @@ static int st33zp24_recv(struct tpm_chip *chip, unsigned char *buf,
>  	}
>  
>  	expected = be32_to_cpu(*(__be32 *)(buf + 2));
> -	if (expected > count) {
> +	if (expected > count || expected < TPM_HEADER_SIZE) {
>  		size = -EIO;
>  		goto out;
>  	}
> diff --git a/drivers/char/tpm/tpm_i2c_infineon.c b/drivers/char/tpm/tpm_i2c_infineon.c
> index 79d6bbb58e39..d5b44cadac56 100644
> --- a/drivers/char/tpm/tpm_i2c_infineon.c
> +++ b/drivers/char/tpm/tpm_i2c_infineon.c
> @@ -473,7 +473,8 @@ static int recv_data(struct tpm_chip *chip, u8 *buf, size_t count)
>  static int tpm_tis_i2c_recv(struct tpm_chip *chip, u8 *buf, size_t count)
>  {
>  	int size = 0;
> -	int expected, status;
> +	int status;
> +	u32 expected;
>  
>  	if (count < TPM_HEADER_SIZE) {
>  		size = -EIO;
> @@ -488,7 +489,7 @@ static int tpm_tis_i2c_recv(struct tpm_chip *chip, u8 *buf, size_t count)
>  	}
>  
>  	expected = be32_to_cpu(*(__be32 *)(buf + 2));
> -	if ((size_t) expected > count) {
> +	if (((size_t) expected > count) || (expected < TPM_HEADER_SIZE)) {
>  		size = -EIO;
>  		goto out;
>  	}
> diff --git a/drivers/char/tpm/tpm_i2c_nuvoton.c b/drivers/char/tpm/tpm_i2c_nuvoton.c
> index c6428771841f..17cf7af9a2c5 100644
> --- a/drivers/char/tpm/tpm_i2c_nuvoton.c
> +++ b/drivers/char/tpm/tpm_i2c_nuvoton.c
> @@ -281,7 +281,8 @@ static int i2c_nuvoton_recv(struct tpm_chip *chip, u8 *buf, size_t count)
>  	struct device *dev = chip->dev.parent;
>  	struct i2c_client *client = to_i2c_client(dev);
>  	s32 rc;
> -	int expected, status, burst_count, retries, size = 0;
> +	int status, burst_count, retries, size = 0;
> +	u32 expected;
>  
>  	if (count < TPM_HEADER_SIZE) {
>  		i2c_nuvoton_ready(chip);    /* return to idle */
> @@ -323,7 +324,7 @@ static int i2c_nuvoton_recv(struct tpm_chip *chip, u8 *buf, size_t count)
>  		 * to machine native
>  		 */
>  		expected = be32_to_cpu(*(__be32 *) (buf + 2));
> -		if (expected > count) {
> +		if (expected > count || expected < size) {
>  			dev_err(dev, "%s() expected > count\n", __func__);
>  			size = -EIO;
>  			continue;
> diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
> index fdde971bc810..7561922bc8f8 100644
> --- a/drivers/char/tpm/tpm_tis_core.c
> +++ b/drivers/char/tpm/tpm_tis_core.c
> @@ -202,7 +202,8 @@ static int tpm_tis_recv(struct tpm_chip *chip, u8 *buf, size_t count)
>  {
>  	struct tpm_tis_data *priv = dev_get_drvdata(&chip->dev);
>  	int size = 0;
> -	int expected, status;
> +	int status;
> +	u32 expected;
>  
>  	if (count < TPM_HEADER_SIZE) {
>  		size = -EIO;
> @@ -217,7 +218,7 @@ static int tpm_tis_recv(struct tpm_chip *chip, u8 *buf, size_t count)
>  	}
>  
>  	expected = be32_to_cpu(*(__be32 *) (buf + 2));
> -	if (expected > count) {
> +	if (expected > count || expected < TPM_HEADER_SIZE) {
>  		size = -EIO;
>  		goto out;
>  	}
> -- 
> 2.12.3

LGTM but should be split into four commits.

/Jarkko