[src/trunk]: src/sys/kern Remove support for '%n' in the kernel printf functi...

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

details:   https://anonhg.NetBSD.org/src/rev/6260df8915a5
branches:  trunk
changeset: 1011783:6260df8915a5
user:      maxv <maxv%NetBSD.org@localhost>
date:      Sat Jul 11 07:14:53 2020 +0000

description:
Remove support for '%n' in the kernel printf functions.

It makes vulnerabilities too easily exploitable, is unused and as a sanity
rule should not be used in the kernel to begin with.

Now, "printf(unfiltered_string);" is much less of a problem.

diffstat:

 sys/kern/subr_prf.c |  19 ++++++++++---------
 1 files changed, 10 insertions(+), 9 deletions(-)

diffs (47 lines):

diff -r 7e9de86abf9a -r 6260df8915a5 sys/kern/subr_prf.c
--- a/sys/kern/subr_prf.c       Sat Jul 11 06:46:19 2020 +0000
+++ b/sys/kern/subr_prf.c       Sat Jul 11 07:14:53 2020 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: subr_prf.c,v 1.184 2020/05/23 23:42:43 ad Exp $        */
+/*     $NetBSD: subr_prf.c,v 1.185 2020/07/11 07:14:53 maxv Exp $      */
 
 /*-
  * Copyright (c) 1986, 1988, 1991, 1993
@@ -37,7 +37,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: subr_prf.c,v 1.184 2020/05/23 23:42:43 ad Exp $");
+__KERNEL_RCSID(0, "$NetBSD: subr_prf.c,v 1.185 2020/07/11 07:14:53 maxv Exp $");
 
 #ifdef _KERNEL_OPT
 #include "opt_ddb.h"
@@ -1373,20 +1373,21 @@
                        base = DEC;
                        goto number;
                case 'n':
+                       /* no %n support in the kernel, consume and skip */
                        if (flags & MAXINT)
-                               *va_arg(ap, intmax_t *) = ret;
+                               (void)va_arg(ap, intmax_t *);
                        else if (flags & PTRINT)
-                               *va_arg(ap, intptr_t *) = ret;
+                               (void)va_arg(ap, intptr_t *);
                        else if (flags & SIZEINT)
-                               *va_arg(ap, ssize_t *) = ret;
+                               (void)va_arg(ap, ssize_t *);
                        else if (flags & QUADINT)
-                               *va_arg(ap, quad_t *) = ret;
+                               (void)va_arg(ap, quad_t *);
                        else if (flags & LONGINT)
-                               *va_arg(ap, long *) = ret;
+                               (void)va_arg(ap, long *);
                        else if (flags & SHORTINT)
-                               *va_arg(ap, short *) = ret;
+                               (void)va_arg(ap, short *);
                        else
-                               *va_arg(ap, int *) = ret;
+                               (void)va_arg(ap, int *);
                        continue;       /* no output */
                case 'O':
                        flags |= LONGINT;