[media] au0828: fix possible race condition in usage of dev->ctrlmsg

The register read function is referencing the dev->ctrlmsg structure outside
of the dev->mutex lock, which can cause corruption of the value if multiple
callers are invoking au0828_readreg() simultaneously.

Use a stack variable to hold the result, and copy the buffer returned by
usb_control_msg() to that variable.

In reality, the whole recv_control_msg() function can probably be collapsed
into au0288_readreg() since it is the only caller.

Also get rid of cmd_msg_dump() since the only case in which the function is
ever called only is ever passed a single byte for the response (and it is
already logged).

Signed-off-by: Devin Heitmueller <dheitmueller@kernellabs.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

1 files changed, 12 insertions, 28 deletions

diff --git a/drivers/media/video/au0828/au0828-core.c b/drivers/media/video/au0828/au0828-core.c
index 65914bc421d0..745a80a798c8 100644
--- a/drivers/media/video/au0828/au0828-core.c
+++ b/drivers/media/video/au0828/au0828-core.c
@@ -56,9 +56,12 @@ static int recv_control_msg(struct au0828_dev *dev, u16 request, u32 value,
 
 u32 au0828_readreg(struct au0828_dev *dev, u16 reg)
 {
-        recv_control_msg(dev, CMD_REQUEST_IN, 0, reg, dev->ctrlmsg, 1);
-        dprintk(8, "%s(0x%04x) = 0x%02x\n", __func__, reg, dev->ctrlmsg[0]);
-        return dev->ctrlmsg[0];
+        u8 result = 0;
+
+        recv_control_msg(dev, CMD_REQUEST_IN, 0, reg, &result, 1);
+        dprintk(8, "%s(0x%04x) = 0x%02x\n", __func__, reg, result);
+
+        return result;
 }
 
 u32 au0828_writereg(struct au0828_dev *dev, u16 reg, u32 val)
@@ -67,24 +70,6 @@ u32 au0828_writereg(struct au0828_dev *dev, u16 reg, u32 val)
         return send_control_msg(dev, CMD_REQUEST_OUT, val, reg);
 }
 
-static void cmd_msg_dump(struct au0828_dev *dev)
-{
-        int i;
-
-        for (i = 0; i < sizeof(dev->ctrlmsg); i += 16)
-                dprintk(2, "%s() %02x %02x %02x %02x %02x %02x %02x %02x "
-                                "%02x %02x %02x %02x %02x %02x %02x %02x\n",
-                        __func__,
-                        dev->ctrlmsg[i+0], dev->ctrlmsg[i+1],
-                        dev->ctrlmsg[i+2], dev->ctrlmsg[i+3],
-                        dev->ctrlmsg[i+4], dev->ctrlmsg[i+5],
-                        dev->ctrlmsg[i+6], dev->ctrlmsg[i+7],
-                        dev->ctrlmsg[i+8], dev->ctrlmsg[i+9],
-                        dev->ctrlmsg[i+10], dev->ctrlmsg[i+11],
-                        dev->ctrlmsg[i+12], dev->ctrlmsg[i+13],
-                        dev->ctrlmsg[i+14], dev->ctrlmsg[i+15]);
-}
-
 static int send_control_msg(struct au0828_dev *dev, u16 request, u32 value,
         u16 index)
 {
@@ -118,24 +103,23 @@ static int recv_control_msg(struct au0828_dev *dev, u16 request, u32 value,
         int status = -ENODEV;
         mutex_lock(&dev->mutex);
         if (dev->usbdev) {
-
-                memset(dev->ctrlmsg, 0, sizeof(dev->ctrlmsg));
-
-                /* cp must be memory that has been allocated by kmalloc */
                 status = usb_control_msg(dev->usbdev,
                                 usb_rcvctrlpipe(dev->usbdev, 0),
                                 request,
                                 USB_DIR_IN | USB_TYPE_VENDOR | USB_RECIP_DEVICE,
                                 value, index,
-                                cp, size, 1000);
+                                dev->ctrlmsg, size, 1000);
 
                 status = min(status, 0);
 
                 if (status < 0) {
                         printk(KERN_ERR "%s() Failed receiving control message, error %d.\n",
                                 __func__, status);
-                } else
-                        cmd_msg_dump(dev);
+                }
+
+                /* the host controller requires heap allocated memory, which
+                   is why we didn't just pass "cp" into usb_control_msg */
+                memcpy(cp, dev->ctrlmsg, size);
         }
         mutex_unlock(&dev->mutex);
         return status;