[PATCH 3/4] staging: comedi: addi_apci_1564: check INSN_CONFIG_DIGITAL_TRIG shift

[Ian Abbott]

The `INSN_CONFIG` comedi instruction with sub-instruction code
`INSN_CONFIG_DIGITAL_TRIG` includes a base channel in `data[3]`. This is
used as a right shift amount for other bitmask values without being
checked.  Shift amounts greater than or equal to 32 will result in
undefined behavior.  Add code to deal with this.

Fixes: 1e15687ea472 ("staging: comedi: addi_apci_1564: add Change-of-State 
interrupt subdevice and required functions"
Cc: <sta...@vger.kernel.org> #3.17+
Signed-off-by: Ian Abbott <abbo...@mev.co.uk>
---
 .../staging/comedi/drivers/addi_apci_1564.c   | 20 +++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/drivers/staging/comedi/drivers/addi_apci_1564.c 
b/drivers/staging/comedi/drivers/addi_apci_1564.c
index 10501fe6bb25..1268ba34be5f 100644
--- a/drivers/staging/comedi/drivers/addi_apci_1564.c
+++ b/drivers/staging/comedi/drivers/addi_apci_1564.c
@@ -331,14 +331,22 @@ static int apci1564_cos_insn_config(struct comedi_device 
*dev,
                                    unsigned int *data)
 {
        struct apci1564_private *devpriv = dev->private;
-       unsigned int shift, oldmask;
+       unsigned int shift, oldmask, himask, lomask;
 
        switch (data[0]) {
        case INSN_CONFIG_DIGITAL_TRIG:
                if (data[1] != 0)
                        return -EINVAL;
                shift = data[3];
-               oldmask = (1U << shift) - 1;
+               if (shift < 32) {
+                       oldmask = (1U << shift) - 1;
+                       himask = data[4] << shift;
+                       lomask = data[5] << shift;
+               } else {
+                       oldmask = 0xffffffffu;
+                       himask = 0;
+                       lomask = 0;
+               }
                switch (data[2]) {
                case COMEDI_DIGITAL_TRIG_DISABLE:
                        devpriv->ctrl = 0;
@@ -362,8 +370,8 @@ static int apci1564_cos_insn_config(struct comedi_device 
*dev,
                                devpriv->mode2 &= oldmask;
                        }
                        /* configure specified channels */
-                       devpriv->mode1 |= data[4] << shift;
-                       devpriv->mode2 |= data[5] << shift;
+                       devpriv->mode1 |= himask;
+                       devpriv->mode2 |= lomask;
                        break;
                case COMEDI_DIGITAL_TRIG_ENABLE_LEVELS:
                        if (devpriv->ctrl != (APCI1564_DI_IRQ_ENA |
@@ -380,8 +388,8 @@ static int apci1564_cos_insn_config(struct comedi_device 
*dev,
                                devpriv->mode2 &= oldmask;
                        }
                        /* configure specified channels */
-                       devpriv->mode1 |= data[4] << shift;
-                       devpriv->mode2 |= data[5] << shift;
+                       devpriv->mode1 |= himask;
+                       devpriv->mode2 |= lomask;
                        break;
                default:
                        return -EINVAL;
-- 
2.27.0