linux-kernel - Re: [PATCH v2] char: tpm: tpm-buf: Add sanity check fallback in read helpers

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Message-ID: <Z_e7jK00SZWSsWOg@kernel.org>
Date: Thu, 10 Apr 2025 15:37:40 +0300
From: Jarkko Sakkinen <jarkko@...nel.org>
To: Purva Yeshi <purvayeshi550@...il.com>
Cc: peterhuewe@....de, jgg@...pe.ca, linux-integrity@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] char: tpm: tpm-buf: Add sanity check fallback in read
 helpers

On Thu, Apr 10, 2025 at 04:04:42PM +0530, Purva Yeshi wrote:
> Fix Smatch-detected issue:
> 
> drivers/char/tpm/tpm-buf.c:208 tpm_buf_read_u8() error:
> uninitialized symbol 'value'.
> drivers/char/tpm/tpm-buf.c:225 tpm_buf_read_u16() error:
> uninitialized symbol 'value'.
> drivers/char/tpm/tpm-buf.c:242 tpm_buf_read_u32() error:
> uninitialized symbol 'value'.
> 
> Zero-initialize the return values in tpm_buf_read_u8(),
> tpm_buf_read_u16(), and tpm_buf_read_u32() to guard against
> uninitialized data in case of a boundary overflow.
> 
> Add defensive initialization ensures the return values are
> always defined, preventing undefined behavior if the unexpected
> happens.
> 
> Signed-off-by: Purva Yeshi <purvayeshi550@...il.com>
> ---
> V1 - https://lore.kernel.org/all/20250409205536.210202-1-purvayeshi550@gmail.com/
> V2 - Update commit message to clarify patch adds a sanity check
> 
>  drivers/char/tpm/tpm-buf.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/char/tpm/tpm-buf.c b/drivers/char/tpm/tpm-buf.c
> index e49a19fea3bd..dc882fc9fa9e 100644
> --- a/drivers/char/tpm/tpm-buf.c
> +++ b/drivers/char/tpm/tpm-buf.c
> @@ -201,7 +201,7 @@ static void tpm_buf_read(struct tpm_buf *buf, off_t *offset, size_t count, void
>   */
>  u8 tpm_buf_read_u8(struct tpm_buf *buf, off_t *offset)
>  {
> -	u8 value;
> +	u8 value = 0;
>  
>  	tpm_buf_read(buf, offset, sizeof(value), &value);
>  
> @@ -218,7 +218,7 @@ EXPORT_SYMBOL_GPL(tpm_buf_read_u8);
>   */
>  u16 tpm_buf_read_u16(struct tpm_buf *buf, off_t *offset)
>  {
> -	u16 value;
> +	u16 value = 0;
>  
>  	tpm_buf_read(buf, offset, sizeof(value), &value);
>  
> @@ -235,7 +235,7 @@ EXPORT_SYMBOL_GPL(tpm_buf_read_u16);
>   */
>  u32 tpm_buf_read_u32(struct tpm_buf *buf, off_t *offset)
>  {
> -	u32 value;
> +	u32 value = 0;
>  
>  	tpm_buf_read(buf, offset, sizeof(value), &value);
>  
> -- 
> 2.34.1
> 
> 

It's good and I think this change is appropriate overall!

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

BR, Jarkko