Re: [PATCH] tpm: infineon: add bounds check in tpm_inf_recv

[Jarkko Sakkinen <jarkko@kernel.org>]

On Sat, Oct 04, 2025 at 09:04:17AM +0000, Shahriyar Jalayeri wrote:
> Add two buffer size validations to prevent buffer
> overflows in tpm_inf_recv():
> 
> 1. Validate that the provided buffer can hold at
>    least the 4-byte header before attempting to
>    read it.

What is this 4 byte header? Please describe what it is.

> 2. Validate that the buffer is large enough to
>    hold the data size reported by the TPM before
>    reading the payload.
> 
> Without these checks, a malicious or malfunctioning
> TPM could cause buffer overflows by reporting data
> sizes larger than the provided buffer, leading to
> memory corruption.
> 
> The error messages include both the expected and
> actual buffer sizes to indicate that the operation
> is aborted.

Paragraphs should be 75 chars per line.

> 
> Signed-off-by: Shahriyar Jalayeri <shahriyar@posteo.de>
> ---

Please version your patches e.g., "git format-patch -v2"

And before diff stat it would be good to have a changelog.


>  drivers/char/tpm/tpm_infineon.c | 19 ++++++++++++++++++-
>  1 file changed, 18 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/char/tpm/tpm_infineon.c b/drivers/char/tpm/tpm_infineon.c
> index 7638b65b8..385bac46a 100644
> --- a/drivers/char/tpm/tpm_infineon.c
> +++ b/drivers/char/tpm/tpm_infineon.c
> @@ -247,11 +247,20 @@ static int tpm_inf_recv(struct tpm_chip *chip, u8 * buf, size_t count)
>  	int i;
>  	int ret;
>  	u32 size = 0;
> +	u32 header_size = 4;

Please don't use local variable for a constant.


>  	number_of_wtx = 0;
>  
>  recv_begin:
> +	if (count < header_size) {
> +		dev_err(&chip->dev,
> +			"Buffer too small (count=%zd, header_size=%u), "
> +			"operation aborted\n",
> +			count, header_size);
> +		return -EIO;
> +	}
> +
>  	/* start receiving header */
> -	for (i = 0; i < 4; i++) {
> +	for (i = 0; i < header_size; i++) {
>  		ret = wait(chip, STAT_RDA);
>  		if (ret)
>  			return -EIO;
> @@ -268,6 +277,14 @@ static int tpm_inf_recv(struct tpm_chip *chip, u8 * buf, size_t count)
>  		/* size of the data received */
>  		size = ((buf[2] << 8) | buf[3]);
>  
> +		if (size > count) {
> +			dev_err(&chip->dev,
> +				"Buffer too small for incoming data "
> +				"(count=%zd, size=%u), operation aborted\n",
> +				count, size);
> +			return -EIO;
> +		}
> +
>  		for (i = 0; i < size; i++) {
>  			wait(chip, STAT_RDA);
>  			buf[i] = tpm_data_in(RDFIFO);
> -- 
> 2.43.0
> 

Other than that, same comments apply as for the previous version.

BR, Jarkko