NetBSD Problem Report #41367

From Manuel.Bouyer@lip6.fr  Wed May  6 16:10:36 2009
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Message-Id: <20090506160950.D1462FBB7@armandeche.soc.lip6.fr>
Date: Wed,  6 May 2009 18:09:50 +0200 (MEST)
From: Manuel.Bouyer@lip6.fr
Reply-To: Manuel.Bouyer@lip6.fr
To: gnats-bugs@gnats.NetBSD.org
Subject: pcap_lookupnet() returns wrong netmask
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>Number:         41367
>Category:       lib
>Synopsis:       pcap_lookupnet() returns wrong netmask
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    lib-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed May 06 16:15:00 +0000 2009
>Originator:     Manuel Bouyer
>Release:        NetBSD 5.0
>Organization:
>Environment:
NetBSD netadmin.lip6.fr 5.0_RC2 NetBSD 5.0_RC2 (XEN3_DOMU) #0: Sat Mar 14 16:24:22 UTC 2009  builds@b1.netbsd.org:/home/builds/ab/netbsd-5/i386/200903140000Z-obj/home/builds/ab/netbsd-5/src/sys/arch/i386/compile/XEN3_DOMU i386
Architecture: i386
Machine: i386
(I confirmed the issue on amd64 5.0_RELEASE system)
>Description:
	I noticed that pkgsrc/net/arpwatch didn't work properly on a
	netbsd-5 machine. I tracked it down to pcap_lookupnet() returning
	the wrong netmask (255.255.255.<last byte of IP address> instead
	of 255.255.255.0). This seems to be because libpcap does't
	initialize the memory before calling SIOCGIFNETMASK and the
	kernel doesn't fill all 4 bytes of the sin_addr (only the
	significant bytes are copied it seems).

	Now I don't know if the bug is really in libpcap no zeroing
	out the memory before ioctl, or the kernel not copying the
	whole sin_addr (maybe both ?)
>How-To-Repeat:
	see above
>Fix:
	this patch fixes arpwatch for me:

Index: inet.c
===================================================================
RCS file: /cvsroot/src/dist/libpcap/inet.c,v
retrieving revision 1.2
diff -u -r1.2 inet.c
--- inet.c	27 Feb 2006 15:53:24 -0000	1.2
+++ inet.c	6 May 2009 15:36:47 -0000
@@ -573,6 +573,12 @@
 	}
 	sin4 = (struct sockaddr_in *)&ifr.ifr_addr;
 	*netp = sin4->sin_addr.s_addr;
+	memset(&ifr, 0, sizeof(ifr));
+#ifdef linux
+	/* XXX Work around Linux kernel bug */
+	ifr.ifr_addr.sa_family = AF_INET;
+#endif
+	(void)strncpy(ifr.ifr_name, device, sizeof(ifr.ifr_name));
 	if (ioctl(fd, SIOCGIFNETMASK, (char *)&ifr) < 0) {
 		(void)snprintf(errbuf, PCAP_ERRBUF_SIZE,
 		    "SIOCGIFNETMASK: %s: %s", device, pcap_strerror(errno));

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