Re: [PATCH] staging: comedi: verify array index is correct before using it

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On 09/07/2020 11:29, Dan Carpenter wrote:
This code reads from the array before verifying that "trig" is a valid
index.  If the index is wildly out of bounds then reading from an
invalid address could lead to an Oops.

Fixes: a8c66b684efa ("staging: comedi: addi_apci_1500: rewrite the subdevice support functions")
Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
---
  drivers/staging/comedi/drivers/addi_apci_1500.c | 10 +++++++---
  1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/staging/comedi/drivers/addi_apci_1500.c b/drivers/staging/comedi/drivers/addi_apci_1500.c
index 45ad4ba92f94..689acd69a1b9 100644
--- a/drivers/staging/comedi/drivers/addi_apci_1500.c
+++ b/drivers/staging/comedi/drivers/addi_apci_1500.c
@@ -456,9 +456,9 @@ static int apci1500_di_cfg_trig(struct comedi_device *dev,
  	unsigned int lo_mask = data[5] << shift;
  	unsigned int chan_mask = hi_mask | lo_mask;
  	unsigned int old_mask = (1 << shift) - 1;
-	unsigned int pm = devpriv->pm[trig] & old_mask;
-	unsigned int pt = devpriv->pt[trig] & old_mask;
-	unsigned int pp = devpriv->pp[trig] & old_mask;
+	unsigned int pm;
+	unsigned int pt;
+	unsigned int pp;
if (trig > 1) {
  		dev_dbg(dev->class_dev,
@@ -471,6 +471,10 @@ static int apci1500_di_cfg_trig(struct comedi_device *dev,
  		return -EINVAL;
  	}
+ pm = devpriv->pm[trig] & old_mask;
+	pt = devpriv->pt[trig] & old_mask;
+	pp = devpriv->pp[trig] & old_mask;
+
  	switch (data[2]) {
  	case COMEDI_DIGITAL_TRIG_DISABLE:
  		/* clear trigger configuration */


Nice catch!

Reviewed-by: Ian Abbott <abbotti@xxxxxxxxx>

--
-=( Ian Abbott <abbotti@xxxxxxxxx> || Web: www.mev.co.uk )=-
-=( MEV Ltd. is a company registered in England & Wales. )=-
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