[PATCH 4.12 28/31] isdn/i4l: fix buffer overflow

[Greg Kroah-Hartman]

4.12-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Annie Cherkaev <annie.cherk@xxxxxxxxx>

commit 9f5af546e6acc30f075828cb58c7f09665033967 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 <jitenmt@xxxxxxxxx>
Signed-off-by: Annie Cherkaev <annie.cherk@xxxxxxxxx>
Cc: Karsten Keil <isdn@xxxxxxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/isdn/i4l/isdn_common.c |    1 +
 drivers/isdn/i4l/isdn_net.c    |    5 ++---
 2 files changed, 3 insertions(+), 3 deletions(-)

--- a/drivers/isdn/i4l/isdn_common.c
+++ b/drivers/isdn/i4l/isdn_common.c
@@ -1379,6 +1379,7 @@ isdn_ioctl(struct file *file, uint cmd,
 			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);
--- a/drivers/isdn/i4l/isdn_net.c
+++ b/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)))