Messages in this thread | | | Date | Thu, 09 Oct 2014 10:02:55 +0100 | From | Ian Abbott <> | Subject | Re: [PATCH] staging: comedi: (regression) channel list must be set for COMEDI_CMD ioctl |
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On 09/10/14 00:13, Hartley Sweeten wrote: > On Wednesday, October 08, 2014 8:09 AM, Ian Abbott wrote: >> `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: c6cd0eefb27b ("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> >> Cc: Bernd Porr <mail@berndporr.me.uk> >> Cc: <stable@vger.kernel.org> # 3.15.y 3.16.y 3.17.y >> --- >> drivers/staging/comedi/comedi_fops.c | 15 +++++++-------- >> 1 file changed, 7 insertions(+), 8 deletions(-) >> >> diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c >> index 495969f..a9b7fe5 100644 >> --- a/drivers/staging/comedi/comedi_fops.c >> +++ b/drivers/staging/comedi/comedi_fops.c >> @@ -1462,10 +1462,6 @@ static int __comedi_get_user_chanlist(struct comedi_device *dev, >> unsigned int *chanlist; >> int ret; >> >> - /* user_chanlist could be NULL for do_cmdtest ioctls */ >> - if (!user_chanlist) >> - return 0; >> - > > I think you need a check here to avoid a NULL pointer getting > passed to the memdup_user(). > > If (!user_chanlist || cmd->chanlist_len == 0) > return -EINVAL; > >> chanlist = memdup_user(user_chanlist, >> cmd->chanlist_len * sizeof(unsigned int)); >> if (IS_ERR(chanlist))
It's fine to pass a NULL pointer to memdup_user(). It won't succeed (returning ERR_PTR(-EFAULT)), but it's fine.
-- -=( Ian Abbott @ MEV Ltd. E-mail: <abbotti@mev.co.uk> )=- -=( Web: http://www.mev.co.uk/ )=-
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