isdn: Disable IIOCDBGVAR

[ Upstream commit 5e22002aa8809e2efab2da95855f73f63e14a36c ]

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/isdn/i4l/isdn_common.c b/drivers/isdn/i4l/isdn_common.c
index 7c6f3f5d9d9a2dc11f7bf2c950b6244b984ef429..66ac7fa6e034d2b15917ba59b2b29d93ace3ff31 100644 (file)
--- 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;