> -----Original Message----- > From: Darren Hart [mailto:[email protected]] > Sent: Tuesday, October 3, 2017 10:20 AM > To: Greg KH <[email protected]> > Cc: Limonciello, Mario <[email protected]>; Andy Shevchenko > <[email protected]>; LKML <[email protected]>; > [email protected]; Andy Lutomirski <[email protected]>; > [email protected]; [email protected] > Subject: Re: [PATCH v3 5/8] platform/x86: dell-wmi-smbios: introduce character > device for userspace > > On Tue, Oct 03, 2017 at 11:26:11AM +0200, Greg KH wrote: > > On Wed, Sep 27, 2017 at 11:02:17PM -0500, Mario Limonciello wrote: > > > +static int dell_wmi_smbios_open(struct inode *inode, struct file *file) > > > +{ > > > + return nonseekable_open(inode, file); > > > +} > > > + > > > +static int dell_wmi_smbios_release(struct inode *inode, struct file > > > *file) > > > +{ > > > + return 0; > > > +} > > > > Why even declare an open/release if you don't do anything with them? > > Just leave them empty. > > > > > +static long dell_wmi_smbios_ioctl(struct file *filp, unsigned int cmd, > > > + unsigned long arg) > > > +{ > > > + void __user *p = (void __user *) arg; > > > + size_t size; > > > + int ret = 0; > > > + > > > + if (_IOC_TYPE(cmd) != DELL_WMI_SMBIOS_IOC) > > > + return -ENOTTY; > > > + > > > + switch (cmd) { > > > + case DELL_WMI_SMBIOS_CALL_CMD: > > > + size = sizeof(struct wmi_calling_interface_buffer); > > > + mutex_lock(&buffer_mutex); > > > + if (copy_from_user(devfs_buffer, p, size)) { > > > + ret = -EFAULT; > > > + goto fail_smbios_cmd; > > > + } > > > + ret = run_wmi_smbios_call(devfs_buffer); > > > > You _are_ checking that your structures are valid here, right? I didn't > > see you really were, so I'll let you go audit your code paths for the > > next set of patches. > > > > But really, ugh, this seems horrible. It's a huge vague data blob going > > both ways, this feels ripe for abuse and other bad things. Do you have > > a working userspace implementation for all of this to publish at the > > same time? > > > > This is the general challenge with WMI support, as it was designed to > provide userspace with a way to talk to the firmware. > > For the more general case going forward the intent is to perform the MOF > parsing in the kernel, which will make it possible to do some automated > buffer validation. > > This particular driver is an intermediate step improving on the > mechanism used for existing devices (libsmbios -> dcdbas -> SMM) to use > the safer WMI entry point (using an op region instead of passing a > physical memory pointer to SMM). > > But, that said... Mario, in lieu of the MOF description of the buffer, > we should be able to do some driver specific validation of this buffer > here. >
As the WMI interface exists today even the MOF doesn't describe the Content of the buffer either. It's a buffer passed from userspace to BIOS and back. I described it as the struct, but I'm not really sure how that can be further validated by the Linux kernel without a checksum. This is no different than how dell-smbios and dcdbas operates. New interfaces will have description that is parsable by MOF.
