staging: comedi: (regression) channel list must be set for COMEDI_CMD ioctl
`do_cmd_ioctl()`, the handler for the `COMEDI_CMD` ioctl can incorrectly call the Comedi subdevice's `do_cmd()` handler with a NULL channel list pointer. This is a regression as the `do_cmd()` handler has never been expected to deal with that, leading to a kernel OOPS when it tries to dereference it. A NULL channel list pointer is allowed for the `COMEDI_CMDTEST` ioctl, handled by `do_cmdtest_ioctl()` and the subdevice's `do_cmdtest()` handler, but not for the `COMEDI_CMD` ioctl and its handlers. Both `do_cmd_ioctl()` and `do_cmdtest_ioctl()` call `__comedi_get_user_chanlist()` to copy the channel list from user memory into dynamically allocated kernel memory and check it for consistency. That function currently returns 0 if the `user_chanlist` parameter (pointing to the channel list in user memory) is NULL. That's fine for `do_cmdtest_ioctl()`, but `do_cmd_ioctl()` incorrectly assumes the kernel copy of the channel list has been set-up correctly. Fix it by not allowing the `user_chanlist` parameter to be NULL in `__comedi_get_user_chanlist()`, and only calling it from `do_cmdtest_ioctl()` if the parameter is non-NULL. Thanks to Bernd Porr for reporting the bug via an initial patch sent privately. Fixes: c6cd0eef ("staging: comedi: comedi_fops: introduce __comedi_get_user_chanlist()") Reported-by:Bernd Porr <mail@berndporr.me.uk> Signed-off-by:
Ian Abbott <abbotti@mev.co.uk> Reviewed-by:
H Hartley Sweeten <hsweeten@visionengravers.com> Cc: Bernd Porr <mail@berndporr.me.uk> Cc: <stable@vger.kernel.org> # 3.15.y 3.16.y 3.17.y Signed-off-by:
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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