usb: core: Use sysfs_emit_at() when showing dynamic IDs

When formatting the dynamic USB device IDs to show to
the user space, instead of scnprintf() function use
sysfs_emit_at(). The functions are equivalent, but
using the latter is recommended as it ensures that
no buffer overruns occur.

Testing the change can be done by assigning new IDs
to the USB driver's sysfs attribute new_id,
and then checking that the same values are returned.

For example:

echo 4533 7515 > /sys/bus/usb/drivers/usbfs/new_id
cat /sys/bus/usb/drivers/usbfs/new_id

The output should match the assigned IDs (4533 7515).

Signed-off-by: Hanne-Lotta Mäenpää <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: hannelotta

drivers/usb/core/driver.c

@@ -119,11 +119,11 @@ ssize_t usb_show_dynids(struct usb_dynids *dynids, char *buf)
 	guard(mutex)(&usb_dynids_lock);
 	list_for_each_entry(dynid, &dynids->list, node)
 		if (dynid->id.bInterfaceClass != 0)
-			count += scnprintf(&buf[count], PAGE_SIZE - count, "%04x %04x %02x\n",
+			count += sysfs_emit_at(&buf[count], count, "%04x %04x %02x\n",
 					   dynid->id.idVendor, dynid->id.idProduct,
 					   dynid->id.bInterfaceClass);
 		else
-			count += scnprintf(&buf[count], PAGE_SIZE - count, "%04x %04x\n",
+			count += sysfs_emit_at(&buf[count], count, "%04x %04x\n",
 					   dynid->id.idVendor, dynid->id.idProduct);
 	return count;
 }