ISDN: cleanups / overflow check

Based on work done by Solar Designer for 2.2

drivers/isdn/i4l/isdn_ppp.c

@@ -706,7 +706,7 @@ isdn_ppp_fill_rq(unsigned char *buf, int len, int proto, int slot)
  *           reports, that there is data
  */
 
-static int
+static ssize_t
 isdn_ppp_read(struct file *file, char *buf, size_t count, loff_t *off)
 {
 	struct ippp_struct *is;
@@ -765,7 +765,7 @@ isdn_ppp_read(struct file *file, char *buf, size_t count, loff_t *off)
  * ipppd wanna write a packet to the card .. non-blocking
  */
 
-static int
+static ssize_t
 isdn_ppp_write(struct file *file, const char *buf, size_t count, loff_t *off)
 {
 	isdn_net_local *lp;

drivers/isdn/pcbit/drv.c

@@ -430,7 +430,7 @@ int pcbit_writecmd(const u_char* buf, int len, int user, int driver, int channel
 	switch(dev->l2_state) {
 	case L2_LWMODE:
 		/* check (size <= rdp_size); write buf into board */
-		if (len > BANK4 + 1)
+		if (len < 0 || len > BANK4 + 1 || len > 1024)
 		{
 			printk("pcbit_writecmd: invalid length %d\n", len);
 			return -EINVAL;