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

[Jarkko Sakkinen <jarkko@kernel.org>]

On Tue, Oct 07, 2025 at 09:07:39AM +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.
> 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.
> 
> Fixes: ebb81fdb3dd0 ("[PATCH] tpm: Support for Infineon TPM")
> Signed-off-by: Shahriyar Jalayeri <shahriyar@posteo.de>
> ---
>  drivers/char/tpm/tpm_infineon.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/char/tpm/tpm_infineon.c b/drivers/char/tpm/tpm_infineon.c
> index 7638b65b8..8b90a8191 100644
> --- a/drivers/char/tpm/tpm_infineon.c
> +++ b/drivers/char/tpm/tpm_infineon.c
> @@ -250,6 +250,11 @@ static int tpm_inf_recv(struct tpm_chip *chip, u8 * buf, size_t count)
>  	number_of_wtx = 0;
>  
>  recv_begin:
> +    /* expect at least 1-byte VL header, 1-byte ctrl-tag, 2-byte data size */
> +	if (count < 4) {
> +		return -EIO;
> +	}
> +
>  	/* start receiving header */
>  	for (i = 0; i < 4; i++) {
>  		ret = wait(chip, STAT_RDA);
> @@ -268,6 +273,10 @@ 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 + 6 > count) {
> +			return -EIO;
> +		}
> +
>  		for (i = 0; i < size; i++) {
>  			wait(chip, STAT_RDA);
>  			buf[i] = tpm_data_in(RDFIFO);
> -- 
> 2.43.0
> 

Nitpick: we don't use curly braces for one line statements.
AFAIK scripts/checkpatch.pl complains about this. Other than that
I don't see any issues.

BR, Jarkko