[src/trunk]: src/sys/compat/common tty_43: Check a bitset from userspace is v...

[nia <nia%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/75f90c128401
branches:  trunk
changeset: 944724:75f90c128401
user:      nia <nia%NetBSD.org@localhost>
date:      Fri Oct 09 10:41:53 2020 +0000

description:
tty_43: Check a bitset from userspace is valid before shifting it

Passing a negative value to these legacy compat ioctls results in
left shift on a negative value which is undefined behaviour and results
in the tty (at least, possibly other things) locking up.

The argument to the ioctl should always be > 0. Return EINVAL otherwise.

While here, adjustments to code style to match current guidelines.

Found by UBSan.

Reported-by: syzbot+39cd551a05298b222756%syzkaller.appspotmail.com@localhost

diffstat:

 sys/compat/common/tty_43.c |  16 ++++++++++------
 1 files changed, 10 insertions(+), 6 deletions(-)

diffs (47 lines):

diff -r e2fcd772c914 -r 75f90c128401 sys/compat/common/tty_43.c
--- a/sys/compat/common/tty_43.c        Fri Oct 09 09:03:55 2020 +0000
+++ b/sys/compat/common/tty_43.c        Fri Oct 09 10:41:53 2020 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: tty_43.c,v 1.37 2020/08/08 19:04:58 christos Exp $     */
+/*     $NetBSD: tty_43.c,v 1.38 2020/10/09 10:41:53 nia Exp $  */
 
 /*-
  * Copyright (c) 2008 The NetBSD Foundation, Inc.
@@ -62,7 +62,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: tty_43.c,v 1.37 2020/08/08 19:04:58 christos Exp $");
+__KERNEL_RCSID(0, "$NetBSD: tty_43.c,v 1.38 2020/10/09 10:41:53 nia Exp $");
 
 #if defined(_KERNEL_OPT)
 #include "opt_compat_netbsd.h"
@@ -220,20 +220,24 @@
        case TIOCLBIC:
        case TIOCLSET: {
                struct termios term;
-               int flags;
+               int argbits, flags;
+
+               argbits = *(int *)data;
+               if (argbits < 0)
+                       return EINVAL;
 
                mutex_spin_enter(&tty_lock);
                term = tp->t_termios;
                flags = ttcompatgetflags(tp);
                switch (com) {
                case TIOCLSET:
-                       tp->t_flags = (flags&0xffff) | (*(int *)data<<16);
+                       tp->t_flags = (flags & 0xffff) | (argbits << 16);
                        break;
                case TIOCLBIS:
-                       tp->t_flags = flags | (*(int *)data<<16);
+                       tp->t_flags = flags | (argbits << 16);
                        break;
                case TIOCLBIC:
-                       tp->t_flags = flags & ~(*(int *)data<<16);
+                       tp->t_flags = flags & ~(argbits << 16);
                        break;
                }
                ttcompatsetlflags(tp, &term);