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For interrupts from badly behaved hardware (as emulated by Syzbot), it
is possible for the Comedi core functions that manage the progress of
asynchronous data acquisition to be called from driver ISRs while no
asynchronous command has been set up, which can cause problems such as
invalid pointer dereferencing or dividing by zero.
Change those functions in the Comedi core to use this pattern: if
`comedi_get_is_subdevice_running(s)` returns `true` then call a safe
version of the function with the same name prefixed with an underscore,
followed by a call to `comedi_put_is_subdevice_running(s)`, otherwise
take some default action.
`comedi_get_is_subdevice_running(s)` returning `true` ensures that the
details of the asynchronous command will not be destroyed before the
matching call to `comedi_put_is_subdevice_running(s)`.
Replace calls to those functions from elsewhere in the Comedi core with
calls to the safe versions of the functions.
The modified functions are: `comedi_buf_read_alloc()`,
`comedi_buf_read_free()`, `comedi_buf_read_n_available()`,
`comedi_buf_read_samples()`, `comedi_buf_write_alloc()`,
`comedi_buf_write_free()`, `comedi_buf_write_samples()`,
`comedi_bytes_per_scan()`, `comedi_event()`, `comedi_handle_events()`,
`comedi_inc_scan_progress()`, `comedi_nsamples_left()`,
`comedi_nscans_left()`.
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Link: https://patch.msgid.link/20251023133001.8439-3-abbotti@mev.co.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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syzbot reports a use-after-free in comedi in the below link, which is
due to comedi gladly removing the allocated async area even though poll
requests are still active on the wait_queue_head inside of it. This can
cause a use-after-free when the poll entries are later triggered or
removed, as the memory for the wait_queue_head has been freed. We need
to check there are no tasks queued on any of the subdevices' wait queues
before allowing the device to be detached by the `COMEDI_DEVCONFIG`
ioctl.
Tasks will read-lock `dev->attach_lock` before adding themselves to the
subdevice wait queue, so fix the problem in the `COMEDI_DEVCONFIG` ioctl
handler by write-locking `dev->attach_lock` before checking that all of
the subdevices are safe to be deleted. This includes testing for any
sleepers on the subdevices' wait queues. It remains locked until the
device has been detached. This requires the `comedi_device_detach()`
function to be refactored slightly, moving the bulk of it into new
function `comedi_device_detach_locked()`.
Note that the refactor of `comedi_device_detach()` results in
`comedi_device_cancel_all()` now being called while `dev->attach_lock`
is write-locked, which wasn't the case previously, but that does not
matter.
Thanks to Jens Axboe for diagnosing the problem and co-developing this
patch.
Cc: stable <stable@kernel.org>
Fixes: 2f3fdcd7ce93 ("staging: comedi: add rw_semaphore to protect against device detachment")
Link: https://lore.kernel.org/all/687bd5fe.a70a0220.693ce.0091.GAE@google.com/
Reported-by: syzbot+01523a0ae5600aef5895@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=01523a0ae5600aef5895
Co-developed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Tested-by: Jens Axboe <axboe@kernel.dk>
Link: https://lore.kernel.org/r/20250722155316.27432-1-abbotti@mev.co.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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