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

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Message-ID: <aMwrH5dWQo9nG1D7@kernel.org>
Date: Thu, 18 Sep 2025 18:54:07 +0300
From: Jarkko Sakkinen <jarkko@...nel.org>
To: Gunnar Kudrjavets <gunnarku@...zon.com>
Cc: peterhuewe@....de, 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()

On Wed, Sep 17, 2025 at 03:29:56PM +0000, Gunnar Kudrjavets wrote:
> 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);
> 
> base-commit: 5aca7966d2a7255ba92fd5e63268dd767b223aa5
> --
> 2.47.3
> 

Thank you.

I just applied the earlier fix, and I'll apply this too (before next
PR).

Reviewed-by: Jarkko Sakkinen <jarkko@...nel.org>

BR, Jarkko