Message-ID: <20240206174437.6pwhaha4loswkih4@pali>
Date: Tue, 6 Feb 2024 18:44:37 +0100
From: Pali Rohár <pali@...nel.org>
To: Chris Morgan <macroalpha82@...il.com>
Cc: Luiz Augusto von Dentz <luiz.dentz@...il.com>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Abhishek Pandit-Subedi <abhishekpandit@...omium.org>,
	linux-input@...r.kernel.org,
	Bluez mailing list <linux-bluetooth@...r.kernel.org>,
	Enric Balletbo i Serra <enric.balletbo@...labora.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Logan Gunthorpe <logang@...tatee.com>,
	Andrey Smirnov <andrew.smirnov@...il.com>,
	Kirill Smelkov <kirr@...edi.com>
Subject: Re: [PATCH] Input: uinput - Add UI_SET_UNIQ ioctl handler

On Tuesday 06 February 2024 11:17:12 Chris Morgan wrote:
> On Mon, Jun 13, 2022 at 02:36:18PM -0700, Luiz Augusto von Dentz wrote:
> > Hi,
> > 
> > On Sun, Mar 22, 2020 at 8:47 AM Pali Rohár <pali.rohar@...il.com> wrote:
> > >
> > > On Wednesday 18 December 2019 12:26:59 Pali Rohár wrote:
> > > > On Wednesday 18 December 2019 12:02:24 Pali Rohár wrote:
> > > > > On Friday 06 December 2019 09:40:48 Dmitry Torokhov wrote:
> > > > > > On Fri, Dec 06, 2019 at 10:11:14AM +0100, Pali Rohár wrote:
> > > > > > > On Thursday 05 December 2019 12:03:05 Abhishek Pandit-Subedi wrote:
> > > > > > > > On Thu, Dec 5, 2019 at 2:52 AM Pali Rohár <pali.rohar@...il.com> wrote:
> > > > > > > > >
> > > > > > > > > On Tuesday 03 December 2019 11:11:12 Dmitry Torokhov wrote:
> > > > > > > > > > On Tue, Dec 03, 2019 at 06:38:21PM +0100, Pali Rohár wrote:
> > > > > > > > > > > On Tuesday 03 December 2019 00:09:47 Pali Rohár wrote:
> > > > > > > > > > >
> > > > > > > > > > > Hi Dmitry!
> > > > > > > > > > >
> > > > > > > > > > > I was looking again at those _IOW defines for ioctl calls and I have
> > > > > > > > > > > another argument why not specify 'char *' in _IOW:
> > > > > > > > > > >
> > > > > > > > > > > All ioctls in _IOW() specify as a third macro argument type which is
> > > > > > > > > > > passed as pointer to the third argument for ioctl() syscall.
> > > > > > > > > > >
> > > > > > > > > > > So e.g.:
> > > > > > > > > > >
> > > > > > > > > > >   #define EVIOCSCLOCKID _IOW('E', 0xa0, int)
> > > > > > > > > > >
> > > > > > > > > > > is called from userspace as:
> > > > > > > > > > >
> > > > > > > > > > >   int val;
> > > > > > > > > > >   ioctl(fd, EVIOCSCLOCKID, &val);
> > > > > > > > > > >
> > > > > > > > > > > Or
> > > > > > > > > > >
> > > > > > > > > > >   #define EVIOCSMASK _IOW('E', 0x93, struct input_mask)
> > > > > > > > > > >
> > > > > > > > > > > is called as:
> > > > > > > > > > >
> > > > > > > > > > >   struct input_mask val;
> > > > > > > > > > >   ioctl(fd, EVIOCSMASK, &val);
> > > > > > > > > > >
> > > > > > > > > > > So basically third argument for _IOW specify size of byte buffer passed
> > > > > > > > > > > as third argument for ioctl(). In _IOW is not specified pointer to
> > > > > > > > > > > struct input_mask, but struct input_mask itself.
> > > > > > > > > > >
> > > > > > > > > > > And in case you define
> > > > > > > > > > >
> > > > > > > > > > >   #define MY_NEW_IOCTL _IOW(UINPUT_IOCTL_BASE, 200, char*)
> > > > > > > > > > >
> > > > > > > > > > > then you by above usage you should pass data as:
> > > > > > > > > > >
> > > > > > > > > > >   char *val = "DATA";
> > > > > > > > > > >   ioctl(fd, MY_NEW_IOCTL, &val);
> > > > > > > > > > >
> > > > > > > > > > > Which is not same as just:
> > > > > > > > > > >
> > > > > > > > > > >   ioctl(fd, MY_NEW_IOCTL, "DATA");
> > > > > > > > > > >
> > > > > > > > > > > As in former case you passed pointer to pointer to data and in later
> > > > > > > > > > > case you passed only pointer to data.
> > > > > > > > > > >
> > > > > > > > > > > It just mean that UI_SET_PHYS is already defined inconsistently which is
> > > > > > > > > > > also reason why compat ioctl for it was introduced.
> > > > > > > > > >
> > > > > > > > > > Yes, you are right. UI_SET_PHYS is messed up. I guess the question is
> > > > > > > > > > what to do with all of this...
> > > > > > > > > >
> > > > > > > > > > Maybe we should define
> > > > > > > > > >
> > > > > > > > > > #define UI_SET_PHYS_STR(len)  _IOC(_IOC_WRITE, UINPUT_IOCTL_BASE, 111, len)
> > > > > > > > > > #define UI_SET_UNIQ_STR(len)  _IOC(_IOC_WRITE, UINPUT_IOCTL_BASE, 112, len)
> > > > > > > > >
> > > > > > > > > I'm not sure if this is ideal. Normally in C strings are nul-termined,
> > > > > > > > > so functions/macros do not take buffer length.
> > > > > > > > Except strncpy, strndup, snprintf, etc. all expect a buffer length. At
> > > > > > >
> > > > > > > This is something different as for these functions you pass buffer and
> > > > > > > length of buffer which is used in write mode -- not for read mode.
> > > > > > >
> > > > > > > > the user to kernel boundary of ioctl, I think we should require size
> > > > > > > > of the user buffer regardless of the data type.
> > > > > > > >
> > > > > > > > > _STR therefore in names looks inconsistent.
> > > > > > > > The _STR suffix is odd (what to name UI_SET_PHYS_STR then??) but
> > > > > > > > requiring the length seems to be common across various ioctls.
> > > > > > > > * input.h requires a length when requesting the phys and uniq
> > > > > > > > (https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/uapi/linux/input.h#n138)
> > > > > > > > * Same with HIDRAW when setting and getting features:
> > > > > > > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/uapi/linux/hidraw.h#n40,
> > > > > > > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/samples/hidraw/hid-example.c#n88
> > > > > > >
> > > > > > > All these ioctls where is passed length are in opposite direction
> > > > > > > (_IOC_READ) as our PHYS and UNIQ (_IOC_WRITE).
> > > > > > >
> > > > > > > I fully agree that when you need to read something from kernel
> > > > > > > (_IOC_READ) and then writing it to userspace, you need to specify length
> > > > > > > of userspace buffer. Exactly same as with userspace functions like
> > > > > > > memcpy, snprintf, etc... as you pointed. Otherwise you get buffer
> > > > > > > overflow as callee does not know length of buffer.
> > > > > > >
> > > > > > > But here we we have there quite different problem, we need to write
> > > > > > > something to kernel from userspace (_IOC_WRITE) and we are passing
> > > > > > > nul-term string. So in this case specifying size is not required as it
> > > > > > > is implicitly specified as part of passed string.
> > > > > >
> > > > > > With the new IOCTL definitions it does not need to be a NULL-terminated
> > > > > > string. It can be a buffer of characters with given length, and kernel
> > > > > > will NULL-terminate as this it what it wants, not what the caller has to
> > > > > > give.
> > > > >
> > > > > Hi Dmitry! I was thinking more about this problem and I will propose
> > > > > alternative solution, but first with details...
> > > > >
> > > > > I think that we should use NULL terminated strings. Or better disallow
> > > > > NULL byte inside string. Reason: all userspace application expects that
> > > > > input device name would be NULL terminated which implies that in the
> > > > > middle of name cannot be NULL byte.
> > > > >
> > > > > So this must apply also for new PHYS / UNIQ ioctl API. If we want in our
> > > > > ioctl API to use buffer + size (with upper bound limit for size) instead
> > > > > of passing NULL term string (with upper bound limit for string size)
> > > > > then kernel have to add a leading NULL byte to string, plus check that
> > > > > in the buffer there is no NULL byte. I guess this a very little
> > > > > complicate code, but nothing which is problematic.
> > > > >
> > > > > And on the userspace part. Now when userspace want to pass constant
> > > > > string for device name, it just call
> > > > >
> > > > >   ioctl(fd, UI_SET_PHYS, "my name of device");
> > > > >
> > > > > After adding a new ioctl with buffer + size API, userspace would have to
> > > > > call:
> > > > >
> > > > >   ioctl(fd, UI_SET_PHYS_STR(strlen("my name of device")), "my name of device");
> > > > >
> > > > > which looks strange, so programmers would had to move device name into
> > > > > new variable:
> > > > >
> > > > >   const char *name = "my name of device";
> > > > >   ioctl(fd, UI_SET_PHYS_STR(strlen(name)), name);
> > > > >
> > > > > For me the old ioctl API looks easier to use (no need for strlen() or
> > > > > extra variable), but this is just my preference of usage -- as it is
> > > > > simpler for me. Maybe you would have different opinion...
> > > > >
> > > > > And now question: Why we have uinput_compat_ioctl()? It is there only
> > > > > because size part of IOCTL number is different on 32bit and 64bit
> > > > > systems. As we know size part of UI_SET_PHYS is wrong and does not make
> > > > > sense...
> > > > >
> > > > > Would not it be better to change size of UI_SET_PHYS to just zero and
> > > > > then when matching ioctl number just ignore size for this UI_SET_PHYS
> > > > > ioctl? Same for UI_BEGIN_FF_UPLOAD_COMPAT and UI_END_FF_UPLOAD_COMPAT
> > > > > added in: https://git.kernel.org/tip/tip/c/7c7da40
> > > > >
> > > > > And we would not have to deal with uinput_compat_ioctl() at all.
> > > >
> > > > Below is example how change for removing UI_SET_PHYS_COMPAT may look
> > > > like. As header file is not changed and UI_SET_PHYS accepts any size
> > > > argument, it therefore accept also 32bit and 64bit integer. So no
> > > > existing 32bit applications which use UI_SET_PHYS on 64bit kernel would
> > > > not be broken...
> > > >
> > > > Is not this better change then introducing a new UI_SET_PHYS_STR ioctl
> > > > number? Because introduction of new IOCTL number has one big
> > > > disadvantage: Userspace applications needs to support fallback to old
> > > > number as older versions of kernels would be in use for a long time. And
> > > > because kernel does not have to remove old IOCTL number for backward
> > > > compatibility there is basically no need for userspace application to
> > > > user new UI_SET_PHYS_STR IOCTL number...
> > >
> > > Hello! I would like to remind this discussion as problem around a new
> > > UI_SET_UNIQ ioctl is not solved yet and uniq property is really useful
> > > for e.g. bluetooth (uinput) devices.
> > >
> > > Dmitry, when you have a time, could you please look at this discussion
> > > and decide how to go ahead?
> > 
> > Have we decided not to move further with these changes? I actually
> > have a bug in BlueZ related to it since right now we are inconsistent
> > with respect to how we handle uhid vs uinput:
> > 
> > https://github.com/bluez/bluez/issues/352
> > 
> > > > diff --git a/drivers/input/misc/uinput.c b/drivers/input/misc/uinput.c
> > > > index fd253781b..b645210d5 100644
> > > > --- a/drivers/input/misc/uinput.c
> > > > +++ b/drivers/input/misc/uinput.c
> > > > @@ -915,22 +915,6 @@ static long uinput_ioctl_handler(struct file *file, unsigned int cmd,
> > > >               retval = uinput_set_bit(arg, propbit, INPUT_PROP_MAX);
> > > >               goto out;
> > > >
> > > > -     case UI_SET_PHYS:
> > > > -             if (udev->state == UIST_CREATED) {
> > > > -                     retval = -EINVAL;
> > > > -                     goto out;
> > > > -             }
> > > > -
> > > > -             phys = strndup_user(p, 1024);
> > > > -             if (IS_ERR(phys)) {
> > > > -                     retval = PTR_ERR(phys);
> > > > -                     goto out;
> > > > -             }
> > > > -
> > > > -             kfree(udev->dev->phys);
> > > > -             udev->dev->phys = phys;
> > > > -             goto out;
> > > > -
> > > >       case UI_BEGIN_FF_UPLOAD:
> > > >               retval = uinput_ff_upload_from_user(p, &ff_up);
> > > >               if (retval)
> > > > @@ -1023,6 +1007,22 @@ static long uinput_ioctl_handler(struct file *file, unsigned int cmd,
> > > >       case UI_ABS_SETUP & ~IOCSIZE_MASK:
> > > >               retval = uinput_abs_setup(udev, p, size);
> > > >               goto out;
> > > > +
> > > > +     case UI_SET_PHYS & ~IOCSIZE_MASK:
> > > > +             if (udev->state == UIST_CREATED) {
> > > > +                     retval = -EINVAL;
> > > > +                     goto out;
> > > > +             }
> > > > +
> > > > +             phys = strndup_user(p, 1024);
> > > > +             if (IS_ERR(phys)) {
> > > > +                     retval = PTR_ERR(phys);
> > > > +                     goto out;
> > > > +             }
> > > > +
> > > > +             kfree(udev->dev->phys);
> > > > +             udev->dev->phys = phys;
> > > > +             goto out;
> > > >       }
> > > >
> > > >       retval = -EINVAL;
> > > > @@ -1042,8 +1042,6 @@ static long uinput_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
> > > >   * These IOCTLs change their size and thus their numbers between
> > > >   * 32 and 64 bits.
> > > >   */
> > > > -#define UI_SET_PHYS_COMPAT           \
> > > > -     _IOW(UINPUT_IOCTL_BASE, 108, compat_uptr_t)
> > > >  #define UI_BEGIN_FF_UPLOAD_COMPAT    \
> > > >       _IOWR(UINPUT_IOCTL_BASE, 200, struct uinput_ff_upload_compat)
> > > >  #define UI_END_FF_UPLOAD_COMPAT              \
> > > > @@ -1053,9 +1051,6 @@ static long uinput_compat_ioctl(struct file *file,
> > > >                               unsigned int cmd, unsigned long arg)
> > > >  {
> > > >       switch (cmd) {
> > > > -     case UI_SET_PHYS_COMPAT:
> > > > -             cmd = UI_SET_PHYS;
> > > > -             break;
> > > >       case UI_BEGIN_FF_UPLOAD_COMPAT:
> > > >               cmd = UI_BEGIN_FF_UPLOAD;
> > > >               break;
> > > > diff --git a/include/uapi/linux/uinput.h b/include/uapi/linux/uinput.h
> > > > index c9e677e3a..6bda2a142 100644
> > > > --- a/include/uapi/linux/uinput.h
> > > > +++ b/include/uapi/linux/uinput.h
> > > > @@ -142,6 +142,8 @@ struct uinput_abs_setup {
> > > >  #define UI_SET_LEDBIT                _IOW(UINPUT_IOCTL_BASE, 105, int)
> > > >  #define UI_SET_SNDBIT                _IOW(UINPUT_IOCTL_BASE, 106, int)
> > > >  #define UI_SET_FFBIT         _IOW(UINPUT_IOCTL_BASE, 107, int)
> > > > +/* Argument is nul-term string and for backward compatibility is there
> > > > + * specified char*, but size argument (char *) is ignored by this ioctl */
> > > >  #define UI_SET_PHYS          _IOW(UINPUT_IOCTL_BASE, 108, char*)
> > > >  #define UI_SET_SWBIT         _IOW(UINPUT_IOCTL_BASE, 109, int)
> > > >  #define UI_SET_PROPBIT               _IOW(UINPUT_IOCTL_BASE, 110, int)
> > > >
> > > >
> > >
> > > --
> > > Pali Rohár
> > > pali.rohar@...il.com
> > 
> > 
> > 
> > -- 
> > Luiz Augusto von Dentz
> 
> Hate to dig a post up from the dead, but I have a use case for this
> ioctl just like the bluez team and would like to see if I can help
> push it across the finish line.
> 
> Unlike this patch series mimicking what is done with the UI_SET_PHYS
> ioctl, I'd like to simply have a fixed size of 64 characters allowed.
> I'm choosing 64 because that's the same size as the uniq value in the
> hid_device struct (specifically it's set as `char uniq[64]`).
> 
> Would such a specific limit be acceptable, and if so it shouldn't have
> all the messy compatible bits like the proposed method here, would it?
> 
> Thank you,
> Chris

In email <20191218112659.crabhqkbcnxd6fo6@...i> (quoted above) I sent a
patch proposal for this issue. But nobody reacted for it yet.

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