linux-kernel - Re: [PATCH] tpm_tis: Fix undefined behavior in tpm_tis_spi_transfer

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Message-ID: <53b303e1-4e75-4fb1-a700-ba4011c02e26@molgen.mpg.de>
Date: Thu, 18 Sep 2025 00:13:05 +0200
From: Paul Menzel <pmenzel@...gen.mpg.de>
To: Gunnar Kudrjavets <gunnarku@...zon.com>
Cc: peterhuewe@....de, jarkko@...nel.org, jgg@...pe.ca,
 kyarlagadda@...dia.com, linux-integrity@...r.kernel.org,
 linux-kernel@...r.kernel.org, Justinien Bouron <jbouron@...zon.com>
Subject: Re: [PATCH] tpm_tis: Fix undefined behavior in
 tpm_tis_spi_transfer_half()

Dear Gunnar,


Thank you very much for your patch.

Am 17.09.25 um 17:29 schrieb Gunnar Kudrjavets:
> When len is 0, the while loop in tpm_tis_spi_transfer_half() never
> executes, leaving ret uninitialized. This will lead to undefined
> behavior when the function returns.
> 
> The issue was introduced when tpm_tis_spi_transfer() was refactored
> to call tpm_tis_spi_transfer_half() or tpm_tis_spi_transfer_full().
> While ret is properly initialized in tpm_tis_spi_transfer_full(), it
> was missed in tpm_tis_spi_transfer_half().
> 
> Initialize ret to 0 at the beginning of the function to ensure
> defined behavior in all code paths.
> 
> Found by GCC 14.2.0 static analyzer with -fanalyzer.
> 
> Fixes: a86a42ac2bd6 ("tpm_tis_spi: Add hardware wait polling")
> Signed-off-by: Gunnar Kudrjavets <gunnarku@...zon.com>
> Reviewed-by: Justinien Bouron <jbouron@...zon.com>
> ---
>   drivers/char/tpm/tpm_tis_spi_main.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/char/tpm/tpm_tis_spi_main.c b/drivers/char/tpm/tpm_tis_spi_main.c
> index 61b42c83ced8..1b6d79662ca1 100644
> --- a/drivers/char/tpm/tpm_tis_spi_main.c
> +++ b/drivers/char/tpm/tpm_tis_spi_main.c
> @@ -85,7 +85,7 @@ static int tpm_tis_spi_transfer_half(struct tpm_tis_data *data,	u32 addr,
>   	struct spi_transfer spi_xfer[3];
>   	struct spi_message m;
>   	u8 transfer_len;
> -	int ret;
> +	int ret = 0;
> 
>   	while (len) {
>   		transfer_len = min_t(u16, len, MAX_SPI_FRAMESIZE);

Reviewed-by: Paul Menzel <pmenzel@...gen.mpg.de>


Kind regards,

Paul