[PATCH] USB: serial: mos7720: improve handling of a kmalloc failure in read_mos_reg()

[PATCH] USB: serial: mos7720: improve handling of a kmalloc failure in read_mos_reg()

[trix]

From: Tom Rix <trix@redhat.com>

clang static analysis reports this problem

mos7720.c:352:2: warning: Undefined or garbage value returned to caller
        return d;
        ^~~~~~~~

In the parport_mos7715_read_data()'s call to read_mos_reg(), 'd' is
only set after the alloc block.

	buf = kmalloc(1, GFP_KERNEL);
	if (!buf)
		return -ENOMEM;

Although the problem is reported in parport_most7715_read_data(),
none of the callee's of read_mos_reg() check the return status.

So move the clearing of data to before the malloc.

Fixes: 0d130367abf5 ("USB: serial: mos7720: fix control-message error handling")
Signed-off-by: Tom Rix <trix@redhat.com>
---
 drivers/usb/serial/mos7720.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/usb/serial/mos7720.c b/drivers/usb/serial/mos7720.c
index 41ee2984a0df..23e8162c768b 100644
--- a/drivers/usb/serial/mos7720.c
+++ b/drivers/usb/serial/mos7720.c
@@ -214,6 +214,7 @@ static int read_mos_reg(struct usb_serial *serial, unsigned int serial_portnum,
 	u8 *buf;
 	int status;
 
+	*data = 0;
 	buf = kmalloc(1, GFP_KERNEL);
 	if (!buf)
 		return -ENOMEM;
@@ -227,7 +228,6 @@ static int read_mos_reg(struct usb_serial *serial, unsigned int serial_portnum,
 			"mos7720: usb_control_msg() failed: %d\n", status);
 		if (status >= 0)
 			status = -EIO;
-		*data = 0;
 	}
 
 	kfree(buf);
-- 
2.27.0

Re: [PATCH] USB: serial: mos7720: improve handling of a kmalloc failure in read_mos_reg()

[Nathan Chancellor]

On Mon, Jan 11, 2021 at 02:09:04PM -0800, trix@redhat.com wrote:
> From: Tom Rix <trix@redhat.com>
> 
> clang static analysis reports this problem
> 
> mos7720.c:352:2: warning: Undefined or garbage value returned to caller
>         return d;
>         ^~~~~~~~
> 
> In the parport_mos7715_read_data()'s call to read_mos_reg(), 'd' is
> only set after the alloc block.
> 
> 	buf = kmalloc(1, GFP_KERNEL);
> 	if (!buf)
> 		return -ENOMEM;
> 
> Although the problem is reported in parport_most7715_read_data(),
> none of the callee's of read_mos_reg() check the return status.
> 
> So move the clearing of data to before the malloc.
> 
> Fixes: 0d130367abf5 ("USB: serial: mos7720: fix control-message error handling")
> Signed-off-by: Tom Rix <trix@redhat.com>

Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>

> ---
>  drivers/usb/serial/mos7720.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/serial/mos7720.c b/drivers/usb/serial/mos7720.c
> index 41ee2984a0df..23e8162c768b 100644
> --- a/drivers/usb/serial/mos7720.c
> +++ b/drivers/usb/serial/mos7720.c
> @@ -214,6 +214,7 @@ static int read_mos_reg(struct usb_serial *serial, unsigned int serial_portnum,
>  	u8 *buf;
>  	int status;
>  
> +	*data = 0;
>  	buf = kmalloc(1, GFP_KERNEL);
>  	if (!buf)
>  		return -ENOMEM;
> @@ -227,7 +228,6 @@ static int read_mos_reg(struct usb_serial *serial, unsigned int serial_portnum,
>  			"mos7720: usb_control_msg() failed: %d\n", status);
>  		if (status >= 0)
>  			status = -EIO;
> -		*data = 0;
>  	}
>  
>  	kfree(buf);
> -- 
> 2.27.0
> 

Re: [PATCH] USB: serial: mos7720: improve handling of a kmalloc failure in read_mos_reg()

[Johan Hovold]

On Mon, Jan 11, 2021 at 02:09:04PM -0800, trix@redhat.com wrote:
> From: Tom Rix <trix@redhat.com>
> 
> clang static analysis reports this problem
> 
> mos7720.c:352:2: warning: Undefined or garbage value returned to caller
>         return d;
>         ^~~~~~~~
> 
> In the parport_mos7715_read_data()'s call to read_mos_reg(), 'd' is
> only set after the alloc block.
> 
> 	buf = kmalloc(1, GFP_KERNEL);
> 	if (!buf)
> 		return -ENOMEM;
> 
> Although the problem is reported in parport_most7715_read_data(),
> none of the callee's of read_mos_reg() check the return status.
> 
> So move the clearing of data to before the malloc.
> 
> Fixes: 0d130367abf5 ("USB: serial: mos7720: fix control-message error handling")
> Signed-off-by: Tom Rix <trix@redhat.com>
> ---
>  drivers/usb/serial/mos7720.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/serial/mos7720.c b/drivers/usb/serial/mos7720.c
> index 41ee2984a0df..23e8162c768b 100644
> --- a/drivers/usb/serial/mos7720.c
> +++ b/drivers/usb/serial/mos7720.c
> @@ -214,6 +214,7 @@ static int read_mos_reg(struct usb_serial *serial, unsigned int serial_portnum,
>  	u8 *buf;
>  	int status;
>  
> +	*data = 0;
>  	buf = kmalloc(1, GFP_KERNEL);
>  	if (!buf)
>  		return -ENOMEM;

I added a clearing of the buffer to this error path instead to avoid the
redundant assignment for every call due to something which will
basically never happen.

> @@ -227,7 +228,6 @@ static int read_mos_reg(struct usb_serial *serial, unsigned int serial_portnum,
>  			"mos7720: usb_control_msg() failed: %d\n", status);
>  		if (status >= 0)
>  			status = -EIO;
> -		*data = 0;
>  	}
>  
>  	kfree(buf);

Johan