From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wang Shanker Subject: Re: [PATCH] ip: add udp_csum, udp6_csum_tx, udp6_csum_rx control flags to ip l2tp add tunnel Date: Wed, 27 Apr 2016 23:33:15 +0800 Message-ID: References: Mime-Version: 1.0 (Mac OS X Mail 9.3 \(3124\)) Content-Type: text/plain; charset=gb2312 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: netdev@vger.kernel.org To: James Chapman Return-path: Received: from mail-pf0-f195.google.com ([209.85.192.195]:33253 "EHLO mail-pf0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753181AbcD0PdR convert rfc822-to-8bit (ORCPT ); Wed, 27 Apr 2016 11:33:17 -0400 Received: by mail-pf0-f195.google.com with SMTP id e190so6101746pfe.0 for ; Wed, 27 Apr 2016 08:33:16 -0700 (PDT) In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: > =D4=DA 2016=C4=EA4=D4=C227=C8=D5=A3=AC20:21=A3=ACJames Chapman =D0=B4=B5=C0=A3=BA >=20 > On 26 April 2016 at 15:15, Wang Shanker w= rote: >> Hi, all >>=20 >> It=A1=AFs my first time to contribute to such an important open sour= ce project. Things began when I upgraded my server, called "Server A", = form ubuntu 14.04 to 16.04, which is shipped with new kernel version, 4= =2E4. After upgrade, I soon found a l2tp tunnel between this server and= another linux server, called "Server B", via ipv6 broke down. Here is = the network topology: >>=20 >> +----------+ +----------+ >> | Server A | -- IPV6 Network -- | Server B | >> +----------+ +----------+ >>=20 >> The l2tp tunnel was encapsulated in udp datagrams. All the configura= tion was normal and could work after I reverted the kernel on Server A = to original version. >>=20 >> Here is what i did to create the tunnel: >>=20 >> ``` >> on Server A: >>=20 >> ip l2tp add tunnel tunnel_id 86 peer_tunnel_id 86 remote 2001:db8::a= aaa local 2001:db8::bbbb udp_sport 1086 udp_dport 1086 >> ip l2tp add session name l2tpeth0 tunnel_id 86 session_id 86 peer_se= ssion_id 86 >> ip l s l2tpeth0 up >>=20 >> on Server B: >>=20 >> ip l2tp add tunnel tunnel_id 86 peer_tunnel_id 86 local 2001:db8::aa= aa remote 2001:db8::bbbb udp_sport 1086 udp_dport 1086 >> ip l2tp add session name l2tpeth0 tunnel_id 86 session_id 86 peer_se= ssion_id 86 >> ip l s l2tpeth0 up >>=20 >> ``` >>=20 >> When I used tcpdump to diagnose the problem, I got such result: >>=20 >> ``` >> on Server A: >>=20 >> arping -i l2tpeth0 -0 1.2.3.4 >>=20 >> on Server B: >>=20 >> tcpdump -i eth0 -n port 1086 -v >>=20 >> 21:35:57.818810 IP6 (flowlabel 0x8f028, hlim 64, next-header UDP (17= ) payload length: 62) 2001:db8::aaaa.1086 > 2001:db8::bbbb.1086: [bad u= dp cksum 0x0000 -> 0x1140!] UDP, length 54 >> 21:35:58.820572 IP6 (flowlabel 0x8f028, hlim 64, next-header UDP (17= ) payload length: 62) 2001:db8::aaaa.1086 > 2001:db8::bbbb.1086: [bad u= dp cksum 0x0000 -> 0x1140!] UDP, length 54 >> 21:35:59.822216 IP6 (flowlabel 0x8f028, hlim 64, next-header UDP (17= ) payload length: 62) 2001:db8::aaaa.1086 > 2001:db8::bbbb.1086: [bad u= dp cksum 0x0000 -> 0x1140!] UDP, length 54 >>=20 >> ``` >>=20 >> After looking into kernel source, I found out that in this commit a = new feature to set udp6 checksum to zero in commit 6b649fe, which added= `L2TP_ATTR_UDP_ZERO_CSUM6_TX` and `L2TP_ATTR_UDP_ZERO_CSUM6_TX`. >>=20 >> As a result, I added `udp_csum`, `udp6_csum_tx`, `udp6_csum_rx` cont= rol flags to `ip l2tp add tunnel` to control those attributes about che= cksum. >>=20 >> Using this to create the tunnel instead on Server A: >>=20 >> ``` >> ip l2tp add tunnel tunnel_id 86 peer_tunnel_id 86 remote 2001:db8::a= aaa local 2001:db8::bbbb udp_sport 1086 udp_dport 1086 udp6_csum_tx on = udp6_csum_rx on >> ``` >>=20 >> I finally got: >>=20 >> ``` >> on Server A: >>=20 >> arping -i l2tpeth0 -0 1.2.3.4 >>=20 >> on Server B: >>=20 >> tcpdump -i eth0 -n port 1086 -v >>=20 >> 22:07:03.844297 IP6 (flowlabel 0x8f028, hlim 64, next-header UDP (17= ) payload length: 62) 2001:db8::aaaa.1086 > 2001:db8::bbbb.1086: [udp s= um ok] UDP, length 54 >> 22:07:04.845717 IP6 (flowlabel 0x8f028, hlim 64, next-header UDP (17= ) payload length: 62) 2001:db8::aaaa.1086 > 2001:db8::bbbb.1086: [udp s= um ok] UDP, length 54 >> 22:07:05.847965 IP6 (flowlabel 0x8f028, hlim 64, next-header UDP (17= ) payload length: 62) 2001:db8::aaaa.1086 > 2001:db8::bbbb.1086: [udp s= um ok] UDP, length 54 >>=20 >> tcpdump -i l2tpeth0 -v >>=20 >> 22:10:35.691326 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has= 1.2.3.4 tell 0.0.0.0, length 28 >> 22:10:36.693627 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has= 1.2.3.4 tell 0.0.0.0, length 28 >> 22:10:37.695010 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has= 1.2.3.4 tell 0.0.0.0, length 28 >> 22:10:38.697121 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has= 1.2.3.4 tell 0.0.0.0, length 28 >>=20 >> ``` >>=20 >> It seems to work. However, is it the real point that should be fixed= and does my patch fix it well? I need your suggestion. >=20 > This seems reasonable to me. It is good to provide user control of > L2TP checksum options. >=20 > However, there is a problem with your patch. The netlink attributes > you are accessing to control checksums are flags, not u8 values. I=A1=AFm not so familiar with kernel code. However, in ``= :=20 ``` /* * ATTR types defined for L2TP */ enum { L2TP_ATTR_NONE, /* no data */ // ... L2TP_ATTR_IP6_DADDR, /* struct in6_addr */ L2TP_ATTR_UDP_ZERO_CSUM6_TX, /* u8 */ L2TP_ATTR_UDP_ZERO_CSUM6_RX, /* u8 */ // ... } ``` isn=A1=AFt L2TP_ATTR_UDP_ZERO_CSUM6_TX a u8 value? Or should I use `add= attr` instead of `addattr8`?=20 >=20 > Maybe the default checksum setting for such l2tp tunnels should be > changed in the l2tp kernel code to match the previous behaviour where > IPv6 checksums were disabled? I think so. However, I=A1=AFm confused with those code. =46rom the name of the attrs `L2TP_ATTR_UDP_ZERO_CSUM6_TX` and `L2TP_AT= TR_UDP_ZERO_CSUM6_RX`, I=20 can tell that when those flags are set, the checksum will be zero. Also= , according to the=20 comment of commit 6b649fe in kernel source, =A1=B0Added new L2TP config= uration options to allow=20 TX and RX of zero checksums in IPv6. Default is not to use them.=A1=B1,= checksums shouldn't have been zero by default. However, in fact, they are. I think there may be = some bugs in kernel source.=20 >=20 >>=20 >>=20 >> --- >> ip/ipl2tp.c | 45 +++++++++++++++++++++++++++++++++++++++++++++ >> 1 file changed, 45 insertions(+) >>=20 >> diff --git a/ip/ipl2tp.c b/ip/ipl2tp.c >> index 3c8ee93..67a6482 100644 >> --- a/ip/ipl2tp.c >> +++ b/ip/ipl2tp.c >> @@ -56,6 +56,8 @@ struct l2tp_parm { >>=20 >> uint16_t pw_type; >> uint16_t mtu; >> + int udp6_csum_tx:1; >> + int udp6_csum_rx:1; >> int udp_csum:1; >> int recv_seq:1; >> int send_seq:1; >> @@ -117,6 +119,9 @@ static int create_tunnel(struct l2tp_parm *p) >> if (p->encap =3D=3D L2TP_ENCAPTYPE_UDP) { >> addattr16(&req.n, 1024, L2TP_ATTR_UDP_SPORT, p->local= _udp_port); >> addattr16(&req.n, 1024, L2TP_ATTR_UDP_DPORT, p->peer_= udp_port); >> + addattr8 (&req.n, 1024, L2TP_ATTR_UDP_CSUM, p->udp_c= sum); >> + addattr8 (&req.n, 1024, L2TP_ATTR_UDP_ZERO_CSUM6_TX,= p->udp6_csum_tx); >> + addattr8 (&req.n, 1024, L2TP_ATTR_UDP_ZERO_CSUM6_RX,= p->udp6_csum_rx); >> } >>=20 >> if (rtnl_talk(&genl_rth, &req.n, NULL, 0) < 0) >> @@ -282,6 +287,14 @@ static int get_response(struct nlmsghdr *n, voi= d *arg) >> p->l2spec_len =3D rta_getattr_u8(attrs[L2TP_ATTR_L2SP= EC_LEN]); >>=20 >> p->udp_csum =3D !!attrs[L2TP_ATTR_UDP_CSUM]; >> + if (attrs[L2TP_ATTR_UDP_ZERO_CSUM6_TX]) >> + p->udp6_csum_tx =3D rta_getattr_u8(attrs[L2TP_ATTR_UDP_ZER= O_CSUM6_TX]); >> + else >> + p->udp6_csum_tx =3D 1; >> + if (attrs[L2TP_ATTR_UDP_ZERO_CSUM6_RX]) >> + p->udp6_csum_rx =3D rta_getattr_u8(attrs[L2TP_ATTR_UDP_ZER= O_CSUM6_RX]); >> + else >> + p->udp6_csum_rx =3D 1; >> if (attrs[L2TP_ATTR_COOKIE]) >> memcpy(p->cookie, RTA_DATA(attrs[L2TP_ATTR_COOKIE]), >> p->cookie_len =3D RTA_PAYLOAD(attrs[L2TP_ATTR_= COOKIE])); >> @@ -470,6 +483,9 @@ static void usage(void) >> fprintf(stderr, " tunnel_id ID peer_tunnel_id ID\n")= ; >> fprintf(stderr, " [ encap { ip | udp } ]\n"); >> fprintf(stderr, " [ udp_sport PORT ] [ udp_dport POR= T ]\n"); >> + fprintf(stderr, " [ udp_csum { on | off } ]\n"); >> + fprintf(stderr, " [ udp6_csum_tx { on | off } ]\n")= ; >> + fprintf(stderr, " [ udp6_csum_rx { on | off } ]\n")= ; >> fprintf(stderr, "Usage: ip l2tp add session [ name NAME ]\n")= ; >> fprintf(stderr, " tunnel_id ID\n"); >> fprintf(stderr, " session_id ID peer_session_id ID\n= "); >> @@ -500,6 +516,8 @@ static int parse_args(int argc, char **argv, int= cmd, struct l2tp_parm *p) >> /* Defaults */ >> p->l2spec_type =3D L2TP_L2SPECTYPE_DEFAULT; >> p->l2spec_len =3D 4; >> + p->udp6_csum_rx =3D 1; >> + p->udp6_csum_tx =3D 1; >>=20 >> while (argc > 0) { >> if (strcmp(*argv, "encap") =3D=3D 0) { >> @@ -569,6 +587,33 @@ static int parse_args(int argc, char **argv, in= t cmd, struct l2tp_parm *p) >> if (get_u16(&uval, *argv, 0)) >> invarg("invalid port\n", *argv); >> p->peer_udp_port =3D uval; >> + } else if (strcmp(*argv, "udp_csum") =3D=3D 0) { >> + NEXT_ARG(); >> + if (strcmp(*argv, "on") =3D=3D 0) { >> + p->udp_csum =3D 1; >> + } else if (strcmp(*argv, "off") =3D=3D 0) { >> + p->udp_csum =3D 0; >> + } else { >> + invarg("invalid option for udp_csum\= n", *argv); >> + } >> + } else if (strcmp(*argv, "udp6_csum_rx") =3D=3D 0) { >> + NEXT_ARG(); >> + if (strcmp(*argv, "on") =3D=3D 0) { >> + p->udp6_csum_rx =3D 1; >> + } else if (strcmp(*argv, "off") =3D=3D 0) { >> + p->udp6_csum_rx =3D 0; >> + } else { >> + invarg("invalid option for udp6_csum= _rx\n", *argv); >> + } >> + } else if (strcmp(*argv, "udp6_csum_tx") =3D=3D 0) { >> + NEXT_ARG(); >> + if (strcmp(*argv, "on") =3D=3D 0) { >> + p->udp6_csum_tx =3D 1; >> + } else if (strcmp(*argv, "off") =3D=3D 0) { >> + p->udp6_csum_tx =3D 0; >> + } else { >> + invarg("invalid option for udp6_csum= _tx\n", *argv); >> + } >> } else if (strcmp(*argv, "offset") =3D=3D 0) { >> __u8 uval; >>=20 >> -- >> 2.5.2 >>=20