[PATCH 4.14 095/193] media: pvrusb2: Prevent a buffer overflow

[Greg Kroah-Hartman]

[ Upstream commit c1ced46c7b49ad7bc064e68d966e0ad303f917fb ]

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: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/media/usb/pvrusb2/pvrusb2-hdw.c | 2 ++
 drivers/media/usb/pvrusb2/pvrusb2-hdw.h | 1 +
 2 files changed, 3 insertions(+)

diff --git a/drivers/media/usb/pvrusb2/pvrusb2-hdw.c b/drivers/media/usb/pvrusb2/pvrusb2-hdw.c
index 44975061b9536..ddededc4ced45 100644
--- a/drivers/media/usb/pvrusb2/pvrusb2-hdw.c
+++ b/drivers/media/usb/pvrusb2/pvrusb2-hdw.c
@@ -666,6 +666,8 @@ static int ctrl_get_input(struct pvr2_ctrl *cptr,int *vp)
 
 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;
 }
 
diff --git a/drivers/media/usb/pvrusb2/pvrusb2-hdw.h b/drivers/media/usb/pvrusb2/pvrusb2-hdw.h
index 25648add77e58..bd2b7a67b7322 100644
--- a/drivers/media/usb/pvrusb2/pvrusb2-hdw.h
+++ b/drivers/media/usb/pvrusb2/pvrusb2-hdw.h
@@ -50,6 +50,7 @@
 #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 */
-- 
2.20.1