[PATCH] eeprom: idt_89hpesx: replace open-coded kmemdup_nul

[PATCH] eeprom: idt_89hpesx: replace open-coded kmemdup_nul

[Justin Stitt]

A malloc + strncpy + manual NUL_termination is just kmemdup_nul. Let's use
this interface as it is less error-prone and more readable.

Also drop `csraddr_len` as it is just used in a single place and we can
just do the arithmetic in-line.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
Link: https://github.com/KSPP/linux/issues/90
Cc: linux-hardening@vger.kernel.org
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Justin Stitt <justinstitt@google.com>
---
Note: build-tested only.
---
 drivers/misc/eeprom/idt_89hpesx.c | 11 +++--------
 1 file changed, 3 insertions(+), 8 deletions(-)

diff --git a/drivers/misc/eeprom/idt_89hpesx.c b/drivers/misc/eeprom/idt_89hpesx.c
index 1d1f30b5c426..d807d08e2614 100644
--- a/drivers/misc/eeprom/idt_89hpesx.c
+++ b/drivers/misc/eeprom/idt_89hpesx.c
@@ -905,7 +905,7 @@ static ssize_t idt_dbgfs_csr_write(struct file *filep, const char __user *ubuf,
 {
 	struct idt_89hpesx_dev *pdev = filep->private_data;
 	char *colon_ch, *csraddr_str, *csrval_str;
-	int ret, csraddr_len;
+	int ret;
 	u32 csraddr, csrval;
 	char *buf;
 
@@ -927,21 +927,16 @@ static ssize_t idt_dbgfs_csr_write(struct file *filep, const char __user *ubuf,
 	 * no new CSR value
 	 */
 	if (colon_ch != NULL) {
-		csraddr_len = colon_ch - buf;
-		csraddr_str =
-			kmalloc(csraddr_len + 1, GFP_KERNEL);
+		/* Copy the register address to the substring buffer */
+		csraddr_str = kmemdup_nul(buf, colon_ch - buf, GFP_KERNEL);
 		if (csraddr_str == NULL) {
 			ret = -ENOMEM;
 			goto free_buf;
 		}
-		/* Copy the register address to the substring buffer */
-		strncpy(csraddr_str, buf, csraddr_len);
-		csraddr_str[csraddr_len] = '\0';
 		/* Register value must follow the colon */
 		csrval_str = colon_ch + 1;
 	} else /* if (str_colon == NULL) */ {
 		csraddr_str = (char *)buf; /* Just to shut warning up */
-		csraddr_len = strnlen(csraddr_str, count);
 		csrval_str = NULL;
 	}
 

---
base-commit: 6465e260f48790807eef06b583b38ca9789b6072
change-id: 20230927-strncpy-drivers-misc-eeprom-idt_89hpesx-c-b09ed5507b7d

Best regards,
--
Justin Stitt <justinstitt@google.com>

Re: [PATCH] eeprom: idt_89hpesx: replace open-coded kmemdup_nul

[Kees Cook]

On Wed, Sep 27, 2023 at 05:37:06AM +0000, Justin Stitt wrote:
> A malloc + strncpy + manual NUL_termination is just kmemdup_nul. Let's use
> this interface as it is less error-prone and more readable.
> 
> Also drop `csraddr_len` as it is just used in a single place and we can
> just do the arithmetic in-line.
> 
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
> Link: https://github.com/KSPP/linux/issues/90
> Cc: linux-hardening@vger.kernel.org
> Cc: Kees Cook <keescook@chromium.org>
> Signed-off-by: Justin Stitt <justinstitt@google.com>

Yup, this looks correct to me. Another good case of using kmemdup_nul().

Reviewed-by: Kees Cook <keescook@chromium.org>

> ---
> Note: build-tested only.
> ---
>  drivers/misc/eeprom/idt_89hpesx.c | 11 +++--------
>  1 file changed, 3 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/misc/eeprom/idt_89hpesx.c b/drivers/misc/eeprom/idt_89hpesx.c
> index 1d1f30b5c426..d807d08e2614 100644
> --- a/drivers/misc/eeprom/idt_89hpesx.c
> +++ b/drivers/misc/eeprom/idt_89hpesx.c
> @@ -905,7 +905,7 @@ static ssize_t idt_dbgfs_csr_write(struct file *filep, const char __user *ubuf,
>  {
>  	struct idt_89hpesx_dev *pdev = filep->private_data;
>  	char *colon_ch, *csraddr_str, *csrval_str;
> -	int ret, csraddr_len;
> +	int ret;
>  	u32 csraddr, csrval;
>  	char *buf;
>  
> @@ -927,21 +927,16 @@ static ssize_t idt_dbgfs_csr_write(struct file *filep, const char __user *ubuf,
>  	 * no new CSR value
>  	 */
>  	if (colon_ch != NULL) {
> -		csraddr_len = colon_ch - buf;
> -		csraddr_str =
> -			kmalloc(csraddr_len + 1, GFP_KERNEL);
> +		/* Copy the register address to the substring buffer */
> +		csraddr_str = kmemdup_nul(buf, colon_ch - buf, GFP_KERNEL);
>  		if (csraddr_str == NULL) {
>  			ret = -ENOMEM;
>  			goto free_buf;
>  		}
> -		/* Copy the register address to the substring buffer */
> -		strncpy(csraddr_str, buf, csraddr_len);
> -		csraddr_str[csraddr_len] = '\0';
>  		/* Register value must follow the colon */
>  		csrval_str = colon_ch + 1;
>  	} else /* if (str_colon == NULL) */ {
>  		csraddr_str = (char *)buf; /* Just to shut warning up */
> -		csraddr_len = strnlen(csraddr_str, count);
>  		csrval_str = NULL;
>  	}
>  
> 
> ---
> base-commit: 6465e260f48790807eef06b583b38ca9789b6072
> change-id: 20230927-strncpy-drivers-misc-eeprom-idt_89hpesx-c-b09ed5507b7d
> 
> Best regards,
> --
> Justin Stitt <justinstitt@google.com>
> 

-- 
Kees Cook