Bug 12847

See PR bin/12448.

Fix: A buffer containing sockaddrs (RTA_DST, RTA_GATEWAY, RTA_NETMASK) 
is passed to and from the kernel. Arp did not align the sockaddrs
when constructing the buffer but the kernel (rtsock.c) required the
starting address of each sockaddr in the buffer to be a multiple of 4.

Arp -s broke when the size of sockaddr_dl (RTA_GATEWAY) increased from
20 to 54 after some new elements were added. So RTA_NETMASK was copied
to and from the wrong offset by rtsock.c (offset 16+56) and arp.c
(offset 16+54).

ROUNDUP() macro is now used in arp.c when copying sockaddr structures to
and from the buffer.

The patch is included below. Please fetch from
http://www.daddylonglegs.com/arp.patch if you encounter problems with
spaces, tabs and newlines.

==========================================cut here============================================
#define SETFUNC(f)    { if (func) usage(); func = (f); }

+ #define ROUNDUP(a) \
+         ((a) > 0 ? (1 + (((a) - 1) | (sizeof(long) - 1))) : sizeof(long))
+
  int
  main(argc, argv)
        int argc;
***************


NEXTADDR(RTA_DST, sin_m);
        NEXTADDR(RTA_GATEWAY, sdl_m);
--- 610,616 ----
        }
  #define NEXTADDR(w, s) \
        if (rtm->rtm_addrs & (w)) { \
!               bcopy((char *)&s, cp, sizeof(s)); cp += ROUNDUP(sizeof(s));}

        NEXTADDR(RTA_DST, sin_m);
        NEXTADDR(RTA_GATEWAY, sdl_m);
============================================cut here========================================--ApYkN7NSFFu5mZzc5hYPFkDkvKSBwVjZywzHQydOxnzylztc
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*** usr.sbin/arp/arp.c.orig     Sun Jun  6 10:26:08 1999
--- usr.sbin/arp/arp.c  Mon Jul 26 18:05:12 1999
***************
*** 112,117 ****
--- 112,120 ----
How-To-Repeat: See PR bin/12448.