isdn: Disable IIOCDBGVAR

It was possible to directly leak the kernel address where the isdn_dev
structure pointer was stored. This is a kernel ASLR bypass for anyone
with access to the ioctl. The code had been present since the beginning
of git history, though this shouldn't ever be needed for normal operation,
therefore remove it.

Reported-by: Al Viro <viro@zeniv.linux.org.uk>
Cc: Karsten Keil <isdn@linux-pingi.de>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 1 insertions, 7 deletions

diff --git a/drivers/isdn/i4l/isdn_common.c b/drivers/isdn/i4l/isdn_common.c
index 7a501dbe7123..6a5b3f00f9ad 100644
--- a/drivers/isdn/i4l/isdn_common.c
+++ b/drivers/isdn/i4l/isdn_common.c
@@ -1640,13 +1640,7 @@ isdn_ioctl(struct file *file, uint cmd, ulong arg)
                         } else
                                 return -EINVAL;
                 case IIOCDBGVAR:
-                        if (arg) {
-                                if (copy_to_user(argp, &dev, sizeof(ulong)))
-                                        return -EFAULT;
-                                return 0;
-                        } else
-                                return -EINVAL;
-                        break;
+                        return -EINVAL;
                 default:
                         if ((cmd & IIOCDRVCTL) == IIOCDRVCTL)
                                 cmd = ((cmd >> _IOC_NRSHIFT) & _IOC_NRMASK) & ISDN_DRVIOCTL_MASK;