`ni_cdio_cmdtest()` validates Comedi asynchronous commands for the DIO subdevice (subdevice 2) of supported National Instruments M-series cards. It is called when handling the `COMEDI_CMD` and `COMEDI_CMDTEST` ioctls for this subdevice. There are two causes for a possible divide-by-zero error when validating that the `stop_arg` member of the passed-in command is not too large. The first cause for the divide-by-zero is that calls to `comedi_bytes_per_scan()` are only valid once the command has been copied to `s->async->cmd`, but that copy is only done for the `COMEDI_CMD` ioctl. For the `COMEDI_CMDTEST` ioctl, it will use whatever was left there by the previous `COMEDI_CMD` ioctl, if any. (This is very likely, as it is usual for the application to use `COMEDI_CMDTEST` before `COMEDI_CMD`.) If there has been no previous, valid `COMEDI_CMD` for this subdevice, then `comedi_bytes_per_scan()` will return 0, so the subsequent division in `ni_cdio_cmdtest()` of `s->async->prealloc_bufsz / comedi_bytes_per_scan(s)` will be a divide-by-zero error. To fix this error, call a new function `comedi_bytes_per_scan_cmd(s, cmd)`, based on the existing `comedi_bytes_per_scan(s)` but using a specified `struct comedi_cmd` for its calculations. (Also refactor `comedi_bytes_per_scan()` to call the new function.) Once the first cause for the divide-by-zero has been fixed, the second cause is that `comedi_bytes_per_scan_cmd()` can legitimately return 0 if the `scan_end_arg` member of the `struct comedi_cmd` being tested is 0. Fix it by only performing the division (and validating that `stop_arg` is no more than the maximum value) if `comedi_bytes_per_scan_cmd()` returns a non-zero value. The problem was reported on the COMEDI mailing list here: https://groups.google.com/forum/#!topic/comedi_list/4t9WlHzMhKM Fixes: f164cbf98fa8 ("staging: comedi: ni_mio_common: add finite regeneration to dio output") Cc: <stable@xxxxxxxxxxxxxxx> # 4.6+ Cc: Spencer E. Olson <olsonse@xxxxxxxxx> Signed-off-by: Ian Abbott <abbotti@xxxxxxxxx> --- drivers/staging/comedi/comedidev.h | 2 ++ drivers/staging/comedi/drivers.c | 33 ++++++++++++++++--- .../staging/comedi/drivers/ni_mio_common.c | 10 ++++-- 3 files changed, 38 insertions(+), 7 deletions(-) diff --git a/drivers/staging/comedi/comedidev.h b/drivers/staging/comedi/comedidev.h index a7d569cfca5d..0dff1ac057cd 100644 --- a/drivers/staging/comedi/comedidev.h +++ b/drivers/staging/comedi/comedidev.h @@ -1001,6 +1001,8 @@ int comedi_dio_insn_config(struct comedi_device *dev, unsigned int mask); unsigned int comedi_dio_update_state(struct comedi_subdevice *s, unsigned int *data); +unsigned int comedi_bytes_per_scan_cmd(struct comedi_subdevice *s, + struct comedi_cmd *cmd); unsigned int comedi_bytes_per_scan(struct comedi_subdevice *s); unsigned int comedi_nscans_left(struct comedi_subdevice *s, unsigned int nscans); diff --git a/drivers/staging/comedi/drivers.c b/drivers/staging/comedi/drivers.c index eefa62f42c0f..5a32b8fc000e 100644 --- a/drivers/staging/comedi/drivers.c +++ b/drivers/staging/comedi/drivers.c @@ -394,11 +394,13 @@ unsigned int comedi_dio_update_state(struct comedi_subdevice *s, EXPORT_SYMBOL_GPL(comedi_dio_update_state); /** - * comedi_bytes_per_scan() - Get length of asynchronous command "scan" in bytes + * comedi_bytes_per_scan_cmd() - Get length of asynchronous command "scan" in + * bytes * @s: COMEDI subdevice. + * @cmd: COMEDI command. * * Determines the overall scan length according to the subdevice type and the - * number of channels in the scan. + * number of channels in the scan for the specified command. * * For digital input, output or input/output subdevices, samples for * multiple channels are assumed to be packed into one or more unsigned @@ -408,9 +410,9 @@ EXPORT_SYMBOL_GPL(comedi_dio_update_state); * * Returns the overall scan length in bytes. */ -unsigned int comedi_bytes_per_scan(struct comedi_subdevice *s) +unsigned int comedi_bytes_per_scan_cmd(struct comedi_subdevice *s, + struct comedi_cmd *cmd) { - struct comedi_cmd *cmd = &s->async->cmd; unsigned int num_samples; unsigned int bits_per_sample; @@ -427,6 +429,29 @@ unsigned int comedi_bytes_per_scan(struct comedi_subdevice *s) } return comedi_samples_to_bytes(s, num_samples); } +EXPORT_SYMBOL_GPL(comedi_bytes_per_scan_cmd); + +/** + * comedi_bytes_per_scan() - Get length of asynchronous command "scan" in bytes + * @s: COMEDI subdevice. + * + * Determines the overall scan length according to the subdevice type and the + * number of channels in the scan for the current command. + * + * For digital input, output or input/output subdevices, samples for + * multiple channels are assumed to be packed into one or more unsigned + * short or unsigned int values according to the subdevice's %SDF_LSAMPL + * flag. For other types of subdevice, samples are assumed to occupy a + * whole unsigned short or unsigned int according to the %SDF_LSAMPL flag. + * + * Returns the overall scan length in bytes. + */ +unsigned int comedi_bytes_per_scan(struct comedi_subdevice *s) +{ + struct comedi_cmd *cmd = &s->async->cmd; + + return comedi_bytes_per_scan_cmd(s, cmd); +} EXPORT_SYMBOL_GPL(comedi_bytes_per_scan); static unsigned int __comedi_nscans_left(struct comedi_subdevice *s, diff --git a/drivers/staging/comedi/drivers/ni_mio_common.c b/drivers/staging/comedi/drivers/ni_mio_common.c index 5edf59ac6706..b04dad8c7092 100644 --- a/drivers/staging/comedi/drivers/ni_mio_common.c +++ b/drivers/staging/comedi/drivers/ni_mio_common.c @@ -3545,6 +3545,7 @@ static int ni_cdio_cmdtest(struct comedi_device *dev, struct comedi_subdevice *s, struct comedi_cmd *cmd) { struct ni_private *devpriv = dev->private; + unsigned int bytes_per_scan; int err = 0; /* Step 1 : check if triggers are trivially valid */ @@ -3579,9 +3580,12 @@ static int ni_cdio_cmdtest(struct comedi_device *dev, err |= comedi_check_trigger_arg_is(&cmd->convert_arg, 0); err |= comedi_check_trigger_arg_is(&cmd->scan_end_arg, cmd->chanlist_len); - err |= comedi_check_trigger_arg_max(&cmd->stop_arg, - s->async->prealloc_bufsz / - comedi_bytes_per_scan(s)); + bytes_per_scan = comedi_bytes_per_scan_cmd(s, cmd); + if (bytes_per_scan) { + err |= comedi_check_trigger_arg_max(&cmd->stop_arg, + s->async->prealloc_bufsz / + bytes_per_scan); + } if (err) return 3; -- 2.20.1
