`comedi_nsamples_left(s, nsamples)` returns the number of samples
remaining to complete an asynchronous command or the passed in
`nsamples`, whichever is lower. However, it goes wrong in the extreme
case of setting the `nsamples` parameter to `UINT_MAX` when the number
of conversions per "scan" (`s->async->cmd.scan_end_arg`) is 1. It uses
`comedi_nscans_remaining(s, nscans)` to determine the number of scans
remaining, or the parameter `nscans`, whichever is lower. To determine
the parameter `nscans`, it divides `nsamples` by the number of
conversions per scan and adds 1. The addition of 1 is to avoid setting
the parameter `nscans` to 0, as `comedi_nscans_remaining(s, nscans)`
treats that value specially. However in the extreme case where
`nsamples` is `UINT_MAX` and the number of samples per scan is 1, the
addition of 1 to `nscans` overflows, producing the unwanted 0.
Fix it by refactoring new a function `__comedi_nscans_remaining(s,
nscans)` out of `comedi_nscans_remaining(s, nscans)`. The new function
does everything except the special handling when `nscans` is 0. Change
`comedi_nsamples_remaining()` to call the new function without adding 1
to `nscans` to avoid the overflow.
This overflow bug doesn't affect any of the current COMEDI drivers. I
stumbled across it while changing to one of the drivers.
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
92d354cbe9