Yes, that looks like the problem. The comments in l2tp.h which indicate that the csum attributes are u8 values are wrong. Code in net/l2tp/l2tp_netlink.c accesses these attributes using nla_get_flag().
Please submit a patch to fix l2tp_tunnel_sock_create(). Include good change notes and your signed-off-by tag so that it gets reviewed. See Documentation/SubmittingPatches if you haven't submitted a kernel patch here before. On 27 April 2016 at 18:06, Wang Shanker <[email protected]> wrote: > > >> 在 2016年4月27日，23:33，Wang Shanker <[email protected]> 写道： >> >> >> >>> 在 2016年4月27日，20:21，James Chapman <[email protected]> 写道： >>> >>> On 26 April 2016 at 15:15, Wang Shanker <[email protected]> wrote: >>>> Hi, all >>>> >>>> It’s my first time to contribute to such an important open source 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, 4.4. 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: >>>> >>>> +----------+ +----------+ >>>> | Server A | -- IPV6 Network -- | Server B | >>>> +----------+ +----------+ >>>> >>>> The l2tp tunnel was encapsulated in udp datagrams. All the configuration >>>> was normal and could work after I reverted the kernel on Server A to >>>> original version. >>>> >>>> Here is what i did to create the tunnel: >>>> >>>> ``` >>>> on Server A: >>>> >>>> ip l2tp add tunnel tunnel_id 86 peer_tunnel_id 86 remote 2001:db8::aaaa >>>> local 2001:db8::bbbb udp_sport 1086 udp_dport 1086 >>>> ip l2tp add session name l2tpeth0 tunnel_id 86 session_id 86 >>>> peer_session_id 86 >>>> ip l s l2tpeth0 up >>>> >>>> on Server B: >>>> >>>> ip l2tp add tunnel tunnel_id 86 peer_tunnel_id 86 local 2001:db8::aaaa >>>> remote 2001:db8::bbbb udp_sport 1086 udp_dport 1086 >>>> ip l2tp add session name l2tpeth0 tunnel_id 86 session_id 86 >>>> peer_session_id 86 >>>> ip l s l2tpeth0 up >>>> >>>> ``` >>>> >>>> When I used tcpdump to diagnose the problem, I got such result: >>>> >>>> ``` >>>> on Server A: >>>> >>>> arping -i l2tpeth0 -0 1.2.3.4 >>>> >>>> on Server B: >>>> >>>> tcpdump -i eth0 -n port 1086 -v >>>> >>>> 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 udp >>>> 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 udp >>>> 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 udp >>>> cksum 0x0000 -> 0x1140!] UDP, length 54 >>>> >>>> ``` >>>> >>>> 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`. >>>> >>>> As a result, I added `udp_csum`, `udp6_csum_tx`, `udp6_csum_rx` control >>>> flags to `ip l2tp add tunnel` to control those attributes about checksum. >>>> >>>> Using this to create the tunnel instead on Server A: >>>> >>>> ``` >>>> ip l2tp add tunnel tunnel_id 86 peer_tunnel_id 86 remote 2001:db8::aaaa >>>> local 2001:db8::bbbb udp_sport 1086 udp_dport 1086 udp6_csum_tx on >>>> udp6_csum_rx on >>>> ``` >>>> >>>> I finally got: >>>> >>>> ``` >>>> on Server A: >>>> >>>> arping -i l2tpeth0 -0 1.2.3.4 >>>> >>>> on Server B: >>>> >>>> tcpdump -i eth0 -n port 1086 -v >>>> >>>> 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 sum >>>> 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 sum >>>> 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 sum >>>> ok] UDP, length 54 >>>> >>>> tcpdump -i l2tpeth0 -v >>>> >>>> 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 >>>> >>>> ``` >>>> >>>> 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. >>> >>> This seems reasonable to me. It is good to provide user control of >>> L2TP checksum options. >>> >>> However, there is a problem with your patch. The netlink attributes >>> you are accessing to control checksums are flags, not u8 values. >> >> I’m not so familiar with kernel code. However, in `<linux/l2tp.h>` : >> >> ``` >> >> /* >> * 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’t L2TP_ATTR_UDP_ZERO_CSUM6_TX a u8 value? Or should I use `addattr` >> instead of `addattr8`? >> >>> >>> 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’m confused with those code. >> >> From the name of the attrs `L2TP_ATTR_UDP_ZERO_CSUM6_TX` and >> `L2TP_ATTR_UDP_ZERO_CSUM6_RX`, I >> can tell that when those flags are set, the checksum will be zero. Also, >> according to the >> comment of commit 6b649fe in kernel source, “Added new L2TP configuration >> options to allow >> TX and RX of zero checksums in IPv6. Default is not to use them.”, checksums >> shouldn't have >> been zero by default. However, in fact, they are. I think there may be some >> bugs in kernel >> source. > > I think I’ve got the bug. Here is the patch for kernel > > --- > net/l2tp/l2tp_core.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c > index afca2eb..6edfa99 100644 > --- a/net/l2tp/l2tp_core.c > +++ b/net/l2tp/l2tp_core.c > @@ -1376,9 +1376,9 @@ static int l2tp_tunnel_sock_create(struct net *net, > memcpy(&udp_conf.peer_ip6, cfg->peer_ip6, > sizeof(udp_conf.peer_ip6)); > udp_conf.use_udp6_tx_checksums = > - cfg->udp6_zero_tx_checksums; > + ! cfg->udp6_zero_tx_checksums; > udp_conf.use_udp6_rx_checksums = > - cfg->udp6_zero_rx_checksums; > + ! cfg->udp6_zero_rx_checksums; > } else > #endif > { > -- > > >>> >>>> >>>> >>>> --- >>>> ip/ipl2tp.c | 45 +++++++++++++++++++++++++++++++++++++++++++++ >>>> 1 file changed, 45 insertions(+) >>>> >>>> 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 { >>>> >>>> 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 == 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_csum); >>>> + 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); >>>> } >>>> >>>> if (rtnl_talk(&genl_rth, &req.n, NULL, 0) < 0) >>>> @@ -282,6 +287,14 @@ static int get_response(struct nlmsghdr *n, void *arg) >>>> p->l2spec_len = rta_getattr_u8(attrs[L2TP_ATTR_L2SPEC_LEN]); >>>> >>>> p->udp_csum = !!attrs[L2TP_ATTR_UDP_CSUM]; >>>> + if (attrs[L2TP_ATTR_UDP_ZERO_CSUM6_TX]) >>>> + p->udp6_csum_tx = >>>> rta_getattr_u8(attrs[L2TP_ATTR_UDP_ZERO_CSUM6_TX]); >>>> + else >>>> + p->udp6_csum_tx = 1; >>>> + if (attrs[L2TP_ATTR_UDP_ZERO_CSUM6_RX]) >>>> + p->udp6_csum_rx = >>>> rta_getattr_u8(attrs[L2TP_ATTR_UDP_ZERO_CSUM6_RX]); >>>> + else >>>> + p->udp6_csum_rx = 1; >>>> if (attrs[L2TP_ATTR_COOKIE]) >>>> memcpy(p->cookie, RTA_DATA(attrs[L2TP_ATTR_COOKIE]), >>>> p->cookie_len = 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 PORT ]\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 = L2TP_L2SPECTYPE_DEFAULT; >>>> p->l2spec_len = 4; >>>> + p->udp6_csum_rx = 1; >>>> + p->udp6_csum_tx = 1; >>>> >>>> while (argc > 0) { >>>> if (strcmp(*argv, "encap") == 0) { >>>> @@ -569,6 +587,33 @@ static int parse_args(int argc, char **argv, int cmd, >>>> struct l2tp_parm *p) >>>> if (get_u16(&uval, *argv, 0)) >>>> invarg("invalid port\n", *argv); >>>> p->peer_udp_port = uval; >>>> + } else if (strcmp(*argv, "udp_csum") == 0) { >>>> + NEXT_ARG(); >>>> + if (strcmp(*argv, "on") == 0) { >>>> + p->udp_csum = 1; >>>> + } else if (strcmp(*argv, "off") == 0) { >>>> + p->udp_csum = 0; >>>> + } else { >>>> + invarg("invalid option for udp_csum\n", >>>> *argv); >>>> + } >>>> + } else if (strcmp(*argv, "udp6_csum_rx") == 0) { >>>> + NEXT_ARG(); >>>> + if (strcmp(*argv, "on") == 0) { >>>> + p->udp6_csum_rx = 1; >>>> + } else if (strcmp(*argv, "off") == 0) { >>>> + p->udp6_csum_rx = 0; >>>> + } else { >>>> + invarg("invalid option for >>>> udp6_csum_rx\n", *argv); >>>> + } >>>> + } else if (strcmp(*argv, "udp6_csum_tx") == 0) { >>>> + NEXT_ARG(); >>>> + if (strcmp(*argv, "on") == 0) { >>>> + p->udp6_csum_tx = 1; >>>> + } else if (strcmp(*argv, "off") == 0) { >>>> + p->udp6_csum_tx = 0; >>>> + } else { >>>> + invarg("invalid option for >>>> udp6_csum_tx\n", *argv); >>>> + } >>>> } else if (strcmp(*argv, "offset") == 0) { >>>> __u8 uval; >>>> >>>> -- >>>> 2.5.2 >
