linux-kernel - Re: [PATCH] char: tpm: tpm-buf: Fix uninitialized return values in read helpers

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Message-ID: <Z_dh4tRIa6xxAWQ2@kernel.org>
Date: Thu, 10 Apr 2025 09:14:58 +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] char: tpm: tpm-buf: Fix uninitialized return values in
 read helpers

On Thu, Apr 10, 2025 at 02:25:36AM +0530, Purva Yeshi wrote:
> Fix Smatch-detected error:
> 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'.
> 
> Call tpm_buf_read() to populate value but do not check its return
> status. If the read fails, value remains uninitialized, causing
> undefined behavior when returned or processed.
> 
> Initialize value to zero to ensure a defined return even if
> tpm_buf_read() fails, avoiding undefined behavior from using
> an uninitialized variable.

How does tpm_buf_read() fail?

> 
> Signed-off-by: Purva Yeshi <purvayeshi550@...il.com>
> ---
>  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
> 

BR, Jarkko