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`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
Reported-by: Ivan Vasilyev <grabesstimme@gmail.com>
Tested-by: Ivan Vasilyev <grabesstimme@gmail.com>
Fixes:
|
||
|---|---|---|
| .. | ||
| drivers | ||
| kcomedilib | ||
| comedi_buf.c | ||
| comedi_compat32.c | ||
| comedi_compat32.h | ||
| comedi_fops.c | ||
| comedi_internal.h | ||
| comedi_pci.c | ||
| comedi_pci.h | ||
| comedi_pcmcia.c | ||
| comedi_pcmcia.h | ||
| comedi_usb.c | ||
| comedi_usb.h | ||
| comedi.h | ||
| comedidev.h | ||
| comedilib.h | ||
| drivers.c | ||
| Kconfig | ||
| Makefile | ||
| proc.c | ||
| range.c | ||
| TODO | ||