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Re: [PATCH v2 3/5] IB/hfi1: Add ioctl() interface for user commands

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On Thu, May 12, 2016 at 03:27:27PM -0400, Dennis Dalessandro wrote:
> >I thought we agreed to get rid of this as well? It certainly does not
> >belong here, and as a general rule, I don't think ioctls should be
> >doing capable tests..
> 
> Yeah. I left it in this patch set because this just "ports" our existing
> code to ioctl(). The eprom stuff is completely removed in another patch set
> that I posted shortly after this. It's at:

Adding code and then removing it in a later patch is not a best
practice.. Just don't add it or define ioctl numbers at all..

> >>+static inline int check_ioctl_access(unsigned int cmd, unsigned long arg)
> >>+{
> >>+	int read_cmd, write_cmd, read_ok, write_ok;
> >>+
> >>+	read_cmd = _IOC_DIR(cmd) & _IOC_READ;
> >>+	write_cmd = _IOC_DIR(cmd) & _IOC_WRITE;
> >>+	write_ok = access_ok(VERIFY_WRITE, (void __user *)arg, _IOC_SIZE(cmd));
> >>+	read_ok = access_ok(VERIFY_READ, (void __user *)arg, _IOC_SIZE(cmd));
> >>+
> >>+	if ((read_cmd && !write_ok) || (write_cmd && !read_ok))
> >>+		return -EFAULT;
> >
> >This seems kind of goofy, didn't Ira say this is performance senstive?

Well, calling access_ok twice when only once is typically needed is
certainly not performant. Typically this check is done at every access
via get_user/put_user/copy_to/from_user - why is it being hoisted like
this?

> >Driver shouldn't be open coding __get_user like that, IMHO.
> 
> Can you explain what you mean here? We should not use __get_user()?

Generally speaking, yes. Use get_user() that includes the correct
access_ok. Unless there is a good reason to avoid it, the standard API
should be used.

> _IOW means user is writing data to the device. So the device is reading data
> from the user. Or am I missing your point?

You are right, I spaced on this when reading the above - 'write_ok'
and 'write_cmd' seem like they should have been related, but really
aren't. It is doing the right tests, just odd. (eg use names like
write_cmd_ok, write_cmd for better clarity)

Jason

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[PATCH v2 0/5] IB/hfi1: Remove write() and use ioctl() for user  access Dennis Dalessandro <dennis.dalessandro@intel.com> - 2016-05-12 19:20 +0200
  [PATCH v2 3/5] IB/hfi1: Add ioctl() interface for user commands Dennis Dalessandro <dennis.dalessandro@intel.com> - 2016-05-12 19:20 +0200
    Re: [PATCH v2 3/5] IB/hfi1: Add ioctl() interface for user commands Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-05-12 19:50 +0200
      RE: [PATCH v2 3/5] IB/hfi1: Add ioctl() interface for user commands "Hefty, Sean" <sean.hefty@intel.com> - 2016-05-12 20:20 +0200
      Re: [PATCH v2 3/5] IB/hfi1: Add ioctl() interface for user commands Dennis Dalessandro <dennis.dalessandro@intel.com> - 2016-05-12 21:30 +0200
        Re: [PATCH v2 3/5] IB/hfi1: Add ioctl() interface for user commands Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-05-12 21:50 +0200
          Re: [PATCH v2 3/5] IB/hfi1: Add ioctl() interface for user commands Doug Ledford <dledford@redhat.com> - 2016-05-12 21:50 +0200
            Re: [PATCH v2 3/5] IB/hfi1: Add ioctl() interface for user commands Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-05-12 23:30 +0200
              Re: [PATCH v2 3/5] IB/hfi1: Add ioctl() interface for user commands Dennis Dalessandro <dennis.dalessandro@intel.com> - 2016-05-13 16:40 +0200
          Re: [PATCH v2 3/5] IB/hfi1: Add ioctl() interface for user commands "ira.weiny" <ira.weiny@intel.com> - 2016-05-13 23:00 +0200
  [PATCH v2 1/5] IB/hfi1: Export drivers user sw version via sysfs Dennis Dalessandro <dennis.dalessandro@intel.com> - 2016-05-12 19:20 +0200
  [PATCH v2 2/5] IB/hfi1: Remove unused user command Dennis Dalessandro <dennis.dalessandro@intel.com> - 2016-05-12 19:20 +0200
  [PATCH v2 4/5] IB/hfi1: Remove write(), use ioctl() for user cmds Dennis Dalessandro <dennis.dalessandro@intel.com> - 2016-05-12 19:20 +0200
  [PATCH v2 5/5] IB/hfi1: Add trace message in user IOCTL handling Dennis Dalessandro <dennis.dalessandro@intel.com> - 2016-05-12 19:20 +0200
  Re: [PATCH v2 0/5] IB/hfi1: Remove write() and use ioctl() for user  access Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-05-12 19:40 +0200
    Re: [PATCH v2 0/5] IB/hfi1: Remove write() and use ioctl() for user access Dennis Dalessandro <dennis.dalessandro@intel.com> - 2016-05-12 21:10 +0200
      Re: [PATCH v2 0/5] IB/hfi1: Remove write() and use ioctl() for user  access Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-05-12 21:30 +0200
        Re: [PATCH v2 0/5] IB/hfi1: Remove write() and use ioctl() for user access Dennis Dalessandro <dennis.dalessandro@intel.com> - 2016-05-12 22:00 +0200
          Re: [PATCH v2 0/5] IB/hfi1: Remove write() and use ioctl() for user  access Doug Ledford <dledford@redhat.com> - 2016-05-12 22:40 +0200
          Re: [PATCH v2 0/5] IB/hfi1: Remove write() and use ioctl() for user  access Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-05-12 23:30 +0200

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