[src/trunk]: src/sys/rump/librump/rumpkern Return early on 0-sized transfers ...

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

details:   https://anonhg.NetBSD.org/src/rev/b2ce960e7c58
branches:  trunk
changeset: 1008910:b2ce960e7c58
user:      kamil <kamil%NetBSD.org@localhost>
date:      Sun Apr 05 15:16:11 2020 +0000

description:
Return early on 0-sized transfers (usually to/from NULL-objects)

This logic is already present in subr_copy.c:copyin_vmspace() and
rumpcopy.c:copyinstr().

This avoids memcpy() calls for NULL objects that is Undefined Behavior,
allowed in the kernel space (-fno-delete-null-pointer-checks), but not
in userland.

Reported by UBSan.

diffstat:

 sys/rump/librump/rumpkern/rumpcopy.c |  16 ++++++++++++++--
 1 files changed, 14 insertions(+), 2 deletions(-)

diffs (58 lines):

diff -r e4a699722c16 -r b2ce960e7c58 sys/rump/librump/rumpkern/rumpcopy.c
--- a/sys/rump/librump/rumpkern/rumpcopy.c      Sun Apr 05 14:53:39 2020 +0000
+++ b/sys/rump/librump/rumpkern/rumpcopy.c      Sun Apr 05 15:16:11 2020 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: rumpcopy.c,v 1.23 2019/04/06 03:06:28 thorpej Exp $    */
+/*     $NetBSD: rumpcopy.c,v 1.24 2020/04/05 15:16:11 kamil Exp $      */
 
 /*
  * Copyright (c) 2009 Antti Kantee.  All Rights Reserved.
@@ -26,7 +26,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: rumpcopy.c,v 1.23 2019/04/06 03:06:28 thorpej Exp $");
+__KERNEL_RCSID(0, "$NetBSD: rumpcopy.c,v 1.24 2020/04/05 15:16:11 kamil Exp $");
 
 #define        __UFETCHSTORE_PRIVATE
 #define        __UCAS_PRIVATE
@@ -45,6 +45,9 @@
 {
        int error = 0;
 
+       if (len == 0)
+               return 0;
+
        if (__predict_false(uaddr == NULL && len)) {
                return EFAULT;
        }
@@ -64,6 +67,9 @@
 {
        int error = 0;
 
+       if (len == 0)
+               return 0;
+
        if (__predict_false(uaddr == NULL && len)) {
                return EFAULT;
        }
@@ -137,6 +143,9 @@
        size_t slen;
        int error;
 
+       if (len == 0)
+               return 0;
+
        if (__predict_false(uaddr == NULL && len)) {
                return EFAULT;
        }
@@ -160,6 +169,9 @@
 kcopy(const void *src, void *dst, size_t len)
 {
 
+       if (len == 0)
+               return 0;
+
        memcpy(dst, src, len);
        return 0;
 }