media: pvrusb2: Prevent a buffer overflow

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@oracle.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

diff --git a/drivers/media/usb/pvrusb2/pvrusb2-hdw.c b/drivers/media/usb/pvrusb2/pvrusb2-hdw.c
index 51112b7988e434464fae81f8333e1be25681fad1..816c85786c2abb830658860c2fbb72b6eec87144 100644 (file)
--- 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 25648add77e58c841ebf03672433cfb2e35da34d..bd2b7a67b7322dd3955d3dc49677625d31d4b969 100644 (file)
--- 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 */