Hi Greg, > Date: 2026-10-17 10:19:59+0200 > From: Greg KH <[email protected]> > > On Fri, Oct 16, 2026 at 12:17:05PM -0700, Dmitry Torokhov wrote: > > Hi Shihuang, > > > > On Sat, Oct 17, 2026 at 01:04:07AM +0800, Shihuang Liu wrote: > > > The pxrc and xpad drivers build the physical path by appending a > > > constant "/input0" suffix with strlcat() after usb_make_path(). > > > > > > In preparation for removing the deprecated strlcat() API[1], > > > replace it with strnlen() followed by strscpy() into the remainder > > > of the buffer, as commit 34b228b739f5 ("HID: usbhid: replace > > > strlcat with better alternatives") did for the usbhid drivers. > > ... > > > usb_make_path(udev, pxrc->phys, sizeof(pxrc->phys)); > > > - strlcat(pxrc->phys, "/input0", sizeof(pxrc->phys)); > > > + len = strnlen(pxrc->phys, sizeof(pxrc->phys)); > > > + strscpy(pxrc->phys + len, "/input0", sizeof(pxrc->phys) - len); > > > > I really dislike this conversion pattern, and I do not want to see it > > open-coded across 18 drivers in this series. > > > > usb_make_path() is just a trivial wrapper around snprintf() that already > > returns the length of the formatted string. Calling usb_make_path(), > > ignoring its return value, rescanning the buffer with strnlen(), and > > then open-coding pointer and size arithmetic for strscpy() (along with > > an extra local variable in every probe function) makes the code much > > uglier and harder to read than what we had before. > > > > All of these USB input drivers already include <linux/usb/input.h>, and > > drivers across other subsystems (drivers/hid/usbhid/, drivers/media/rc/, > > drivers/media/usb/, sound/usb/caiaq/, drivers/usb/storage/onetouch.c) > > all use the exact same usb_make_path() + suffix pattern ("/input0", > > "/input%d", "/ir0", "/button", etc.). > > > > If we want to get rid of strlcat() here, please introduce a generic > > helper in include/linux/usb.h (or a USB input helper in > > include/linux/usb/input.h) that formats the USB path together with the > > subpath in a single pass, for example: > > > > __printf(4, 5) > > int usb_make_subpath(struct usb_device *dev, char *buf, size_t size, > > const char *fmt, ...); > > > > (or a simple const char *suffix variant if formatting is not needed). > > Then each driver can do: > > > > usb_make_subpath(udev, pxrc->phys, sizeof(pxrc->phys), "input0"); > > > > and even drivers/hid/usbhid/hid-core.c can simply do: > > > > usb_make_subpath(dev, hid->phys, sizeof(hid->phys), > > "input%d", intf->altsetting[0].desc.bInterfaceNumber); > > > > instead of repeating this strnlen() + strscpy() boilerplate everywhere. > > I'm all for that too, and putting it in the USB core for everyone to use > would be great.
You might be interested in <https://lore.kernel.org/linux-hardening/[email protected]/>. I was working on something like that, but actually much simpler. It is meant to replace strscpy()/snprintf() by versions more similar to Plan9's strecpy(2)/seprint(2), but without some important flaw that the Plan9 APIs have (about handling NULL). Have a lovely day! Alex > > thanks, > > greg k-h > -- <https://www.alejandro-colomar.es>
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