[PATCH] libertas_tf: prevent underflow in process_cmdrequest()

[Dan Carpenter]

If recvlength is less than MESSAGE_HEADER_LEN (4) we would end up
corrupting memory.

Fixes: c305a19a0d0a ("libertas_tf: usb specific functions")
Signed-off-by: Dan Carpenter <dan.carpen...@oracle.com>
---
This is from static analysis.  I'm not positive that this is a real
bug, but it's harmless to check.

diff --git a/drivers/net/wireless/marvell/libertas_tf/if_usb.c 
b/drivers/net/wireless/marvell/libertas_tf/if_usb.c
index e92fc5001171..789337ea676a 100644
--- a/drivers/net/wireless/marvell/libertas_tf/if_usb.c
+++ b/drivers/net/wireless/marvell/libertas_tf/if_usb.c
@@ -605,9 +605,10 @@ static inline void process_cmdrequest(int recvlength, 
uint8_t *recvbuff,
 {
        unsigned long flags;
 
-       if (recvlength > LBS_CMD_BUFFER_SIZE) {
+       if (recvlength < MESSAGE_HEADER_LEN ||
+           recvlength > LBS_CMD_BUFFER_SIZE) {
                lbtf_deb_usbd(&cardp->udev->dev,
-                            "The receive buffer is too large\n");
+                            "The receive buffer is invalid: %d\n", recvlength);
                kfree_skb(skb);
                return;
        }