[PATCH v2] eeprom: idt_89hpesx: uninitialized data in idt_dbgfs_csr_write()

[PATCH v2] eeprom: idt_89hpesx: uninitialized data in idt_dbgfs_csr_write()

[Dan Carpenter]

The simple_write_to_buffer() function will return positive/success if it
is able to write a single byte anywhere within the buffer.  However that
potentially leaves a lot of the buffer uninitialized.

In this code it's better to return 0 if the offset is non-zero.  This
code is not written to support partial writes.  And then return -EFAULT
if the buffer is not completely initialized.

Fixes: cfad6425382e ("eeprom: Add IDT 89HPESx EEPROM/CSR driver")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
---
v2: In v1, I tried to be fancy and use strndup_user().  That potentially
breaks the user space API.  I cannot test this code so it's better to be
conservative.

 drivers/misc/eeprom/idt_89hpesx.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/misc/eeprom/idt_89hpesx.c b/drivers/misc/eeprom/idt_89hpesx.c
index b0cff4b152da..7f430742ce2b 100644
--- a/drivers/misc/eeprom/idt_89hpesx.c
+++ b/drivers/misc/eeprom/idt_89hpesx.c
@@ -909,14 +909,18 @@ static ssize_t idt_dbgfs_csr_write(struct file *filep, const char __user *ubuf,
 	u32 csraddr, csrval;
 	char *buf;
 
+	if (*offp)
+		return 0;
+
 	/* Copy data from User-space */
 	buf = kmalloc(count + 1, GFP_KERNEL);
 	if (!buf)
 		return -ENOMEM;
 
-	ret = simple_write_to_buffer(buf, count, offp, ubuf, count);
-	if (ret < 0)
+	if (copy_from_user(buf, ubuf, count)) {
+		ret = -EFAULT;
 		goto free_buf;
+	}
 	buf[count] = 0;
 
 	/* Find position of colon in the buffer */
-- 
2.35.1

Re: [PATCH v2] eeprom: idt_89hpesx: uninitialized data in idt_dbgfs_csr_write()

[Serge Semin]

On Fri, Jul 08, 2022 at 04:46:38PM +0300, Dan Carpenter wrote:
> The simple_write_to_buffer() function will return positive/success if it
> is able to write a single byte anywhere within the buffer.  However that
> potentially leaves a lot of the buffer uninitialized.
> 
> In this code it's better to return 0 if the offset is non-zero.  This
> code is not written to support partial writes.  And then return -EFAULT
> if the buffer is not completely initialized.
> 
> Fixes: cfad6425382e ("eeprom: Add IDT 89HPESx EEPROM/CSR driver")
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>

Seems reasonable. Thanks.

Reviewed-by: Serge Semin <fancer.lancer@gmail.com>

-Sergey

> ---
> v2: In v1, I tried to be fancy and use strndup_user().  That potentially
> breaks the user space API.  I cannot test this code so it's better to be
> conservative.
> 
>  drivers/misc/eeprom/idt_89hpesx.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/misc/eeprom/idt_89hpesx.c b/drivers/misc/eeprom/idt_89hpesx.c
> index b0cff4b152da..7f430742ce2b 100644
> --- a/drivers/misc/eeprom/idt_89hpesx.c
> +++ b/drivers/misc/eeprom/idt_89hpesx.c
> @@ -909,14 +909,18 @@ static ssize_t idt_dbgfs_csr_write(struct file *filep, const char __user *ubuf,
>  	u32 csraddr, csrval;
>  	char *buf;
>  
> +	if (*offp)
> +		return 0;
> +
>  	/* Copy data from User-space */
>  	buf = kmalloc(count + 1, GFP_KERNEL);
>  	if (!buf)
>  		return -ENOMEM;
>  
> -	ret = simple_write_to_buffer(buf, count, offp, ubuf, count);
> -	if (ret < 0)
> +	if (copy_from_user(buf, ubuf, count)) {
> +		ret = -EFAULT;
>  		goto free_buf;
> +	}
>  	buf[count] = 0;
>  
>  	/* Find position of colon in the buffer */
> -- 
> 2.35.1
>