[PATCH 3.16 041/132] media: pvrusb2: Prevent a buffer overflow

[Ben Hutchings]

3.16.74-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Dan Carpenter <dan.carpenter@xxxxxxxxxx>

commit c1ced46c7b49ad7bc064e68d966e0ad303f917fb upstream.

The ctrl_check_input() function is called from pvr2_ctrl_range_check().
It's supposed to validate user supplied input and return true or false
depending on whether the input is valid or not.  The problem is that
negative shifts or shifts greater than 31 are undefined in C.  In
practice with GCC they result in shift wrapping so this function returns
true for some inputs which are not valid and this could result in a
buffer overflow:

    drivers/media/usb/pvrusb2/pvrusb2-ctrl.c:205 pvr2_ctrl_get_valname()
    warn: uncapped user index 'names[val]'

The cptr->hdw->input_allowed_mask mask is configured in pvr2_hdw_create()
and the highest valid bit is BIT(4).

Fixes: 7fb20fa38caa ("V4L/DVB (7299): pvrusb2: Improve logic which handles input choice availability")

Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xxxxxxxxx>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@xxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 drivers/media/usb/pvrusb2/pvrusb2-hdw.c | 2 ++
 drivers/media/usb/pvrusb2/pvrusb2-hdw.h | 1 +
 2 files changed, 3 insertions(+)

--- a/drivers/media/usb/pvrusb2/pvrusb2-hdw.c
+++ b/drivers/media/usb/pvrusb2/pvrusb2-hdw.c
@@ -670,6 +670,8 @@ static int ctrl_get_input(struct pvr2_ct
 
 static int ctrl_check_input(struct pvr2_ctrl *cptr,int v)
 {
+	if (v < 0 || v > PVR2_CVAL_INPUT_MAX)
+		return 0;
 	return ((1 << v) & cptr->hdw->input_allowed_mask) != 0;
 }
 
--- a/drivers/media/usb/pvrusb2/pvrusb2-hdw.h
+++ b/drivers/media/usb/pvrusb2/pvrusb2-hdw.h
@@ -54,6 +54,7 @@
 #define PVR2_CVAL_INPUT_COMPOSITE 2
 #define PVR2_CVAL_INPUT_SVIDEO 3
 #define PVR2_CVAL_INPUT_RADIO 4
+#define PVR2_CVAL_INPUT_MAX PVR2_CVAL_INPUT_RADIO
 
 enum pvr2_config {
 	pvr2_config_empty,    /* No configuration */