When adding the extra 10% of space to a needed sysctl buffer use math

that is less likely to overflow the int type used. A BGP fullfeed is
now so big that this calculation overflowed and then got sign extended.
The result was for example 'route -n show' failures.
Problem identified with deraadt@
OK deraadt@ (more cleanup needed but this fix is a good start)

diff --git a/sys/net/rtsock.c b/sys/net/rtsock.c
index a717d11..b35beb2 100644 (file)
--- a/sys/net/rtsock.c
+++ b/sys/net/rtsock.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: rtsock.c,v 1.322 2021/09/14 09:15:55 mvs Exp $        */
+/*     $OpenBSD: rtsock.c,v 1.323 2021/12/16 09:33:56 claudio Exp $    */
 /*     $NetBSD: rtsock.c,v 1.18 1996/03/29 00:32:10 cgd Exp $  */
 
 /*
@@ -2219,7 +2219,7 @@ sysctl_rtable(int *name, u_int namelen, void *where, size_t *given, void *new,
                if (*given < w.w_needed)
                        return (ENOMEM);
        } else
-               *given = (11 * w.w_needed) / 10;
+               *given = w.w_needed + w.w_needed / 10;
 
        return (error);
 }