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staging: comedi: ni_mio_common: Fix divide-by-zero for DIO cmdtest

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commit bafd9c6405 upstream.

`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: f164cbf98f ("staging: comedi: ni_mio_common: add finite regeneration to dio output")
Cc: <stable@vger.kernel.org> # 4.6+
Cc: Spencer E. Olson <olsonse@umich.edu>
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Ian Abbott 2019-03-04 14:33:54 +00:00 committed by Greg Kroah-Hartman
parent 4f49089456
commit 7787d64470
3 changed files with 38 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
drivers/staging/comedi/comedidev.h
View File

@ -992,6 +992,8 @@ 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);

33
drivers/staging/comedi/drivers.c
View File

@ -390,11 +390,13 @@ 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
@ -404,9 +406,9 @@ 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;
@ -423,6 +425,29 @@ 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,

10
drivers/staging/comedi/drivers/ni_mio_common.c
View File

@ -3523,6 +3523,7 @@ static int ni_cdio_check_chanlist(struct comedi_device *dev,
static int ni_cdio_cmdtest(struct comedi_device *dev,
struct comedi_subdevice *s, struct comedi_cmd *cmd)
{
unsigned int bytes_per_scan;
int err = 0;
int tmp;
@ -3552,9 +3553,12 @@ 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;