isdn/i4l: fix buffer overflow

commit 9f5af54 upstream.

This fixes a potential buffer overflow in isdn_net.c caused by an
unbounded strcpy.

[ ISDN seems to be effectively unmaintained, and the I4L driver in
  particular is long deprecated, but in case somebody uses this..
    - Linus ]

Signed-off-by: Jiten Thakkar <[email protected]>
Signed-off-by: Annie Cherkaev <[email protected]>
Cc: Karsten Keil <[email protected]>
Cc: Kees Cook <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: anniecherk

drivers/isdn/i4l/isdn_common.c

@@ -1379,6 +1379,7 @@ isdn_ioctl(struct file *file, uint cmd, ulong arg)
 			if (arg) {
 				if (copy_from_user(bname, argp, sizeof(bname) - 1))
 					return -EFAULT;
+				bname[sizeof(bname)-1] = 0;
 			} else
 				return -EINVAL;
 			ret = mutex_lock_interruptible(&dev->mtx);

drivers/isdn/i4l/isdn_net.c

@@ -2611,10 +2611,9 @@ isdn_net_newslave(char *parm)
 	char newname[10];
 
 	if (p) {
-		/* Slave-Name MUST not be empty */
-		if (!strlen(p + 1))
+		/* Slave-Name MUST not be empty or overflow 'newname' */
+		if (strscpy(newname, p + 1, sizeof(newname)) <= 0)
 			return NULL;
-		strcpy(newname, p + 1);
 		*p = 0;
 		/* Master must already exist */
 		if (!(n = isdn_net_findif(parm)))