On Mon, 25 Jun 2018, Joe Perches wrote:

On Tue, 2018-06-26 at 09:16 +0800, Chengguang Xu wrote:

quoted

sizeof() will return unsigned value so in the error check
negative error code will be always larger than sizeof().

This looks like a general class of error in the kernel
where a signed result that could be returning a -errno
is tested against < or <= sizeof()

A couple examples:

drivers/input/mouse/elan_i2c_smbus.c:

		len = i2c_smbus_read_block_data(client,
						ETP_SMBUS_IAP_PASSWORD_READ,
						val);
		if (len < sizeof(u16)) {

i2c_smbus_read_block_data can return a negative errno


net/smc/smc_clc.c:

	len = kernel_sendmsg(smc->clcsock, &msg, &vec, 1,
			     sizeof(struct smc_clc_msg_decline));
	if (len < sizeof(struct smc_clc_msg_decline))

where kernel_sendmsg can return a negative errno

There are probably others, I didn't look hard.

Perhaps a cocci script to find these could be generated?

Here's another one:

drivers/usb/serial/ir-usb.c

@@ -126,13 +126,8 @@ irda_usb_find_class_desc(struct usb_seri
 	if (!desc)
 		return NULL;

-	ret = usb_control_msg(dev, usb_rcvctrlpipe(dev, 0),
-			USB_REQ_CS_IRDA_GET_CLASS_DESC,
-			USB_DIR_IN | USB_TYPE_CLASS | USB_RECIP_INTERFACE,
-			0, ifnum, desc, sizeof(*desc), 1000);

 	dev_dbg(&serial->dev->dev, "%s -  ret=%d\n", __func__, ret);
-	if (ret < sizeof(*desc)) {
 		dev_dbg(&serial->dev->dev,
 			"%s - class descriptor read %s (%d)\n", __func__,
 			(ret < 0) ? "failed" : "too short", ret);

There are other results, but I haven't checked all of them.

julia