The branch main has been updated by vangyzen:
URL:
https://cgit.FreeBSD.org/src/commit/?id=a9f5b68837094699a3d5204d79c1cbe59d93ae00
commit a9f5b68837094699a3d5204d79c1cbe59d93ae00
Author: Eric van Gyzen <vangy...@freebsd.org>
AuthorDate: 2025-08-08 21:59:31 +0000
Commit: Eric van Gyzen <vangy...@freebsd.org>
CommitDate: 2025-08-12 14:38:55 +0000
IPv6: Ignore PTB packets with an MTU < 1280
RFC 2460 section 5 paragraph 7 allowed a Packet Too Big message
to report a Next-Hop MTU less than 1280 in support of 6-to-4 routers.
A node receiving such a message was required to add a Fragment
Header to outgoing packets, even though they were not fragmented.
Almost 20 years later, RFC 8200 was published. It obsoletes RFC 2460
and removes that paragraph. UNH IOL Intact was updated to test for
compliance with the new standard.
Remove code supporting that obsolete paragraph.
Test cases v6LC_4_1_06a and 06b failed before this change, saying:
DUT processed PTB and sent a fragmented echo reply
Those two test cases now pass:
DUT did not process PTB and sent un-fragmented echo reply
All PMTU test cases pass except v6LC_4_1_08. It fails because we
ignore the MTU in RAs.
Reviewed by: tuexen
MFC After: 1 month
Sponsored by: Dell Inc.
Differential Revision: https://reviews.freebsd.org/D51835
---
sys/netinet/icmp6.h | 3 --
sys/netinet/tcp_subr.c | 2 +-
sys/netinet6/icmp6.c | 38 +++-------------
sys/netinet6/ip6_output.c | 107 +++++++++++++++-------------------------------
4 files changed, 40 insertions(+), 110 deletions(-)
diff --git a/sys/netinet/icmp6.h b/sys/netinet/icmp6.h
index 7845b682f3e4..2ca5b3433e47 100644
--- a/sys/netinet/icmp6.h
+++ b/sys/netinet/icmp6.h
@@ -713,9 +713,6 @@ void icmp6_redirect_input(struct mbuf *, int);
void icmp6_redirect_output(struct mbuf *, struct nhop_object *);
int icmp6_ratelimit(const struct in6_addr *, const int, const int);
-struct ip6ctlparam;
-void icmp6_mtudisc_update(struct ip6ctlparam *, int);
-
/* XXX: is this the right place for these macros? */
#define icmp6_ifstat_inc(ifp, tag) \
do { \
diff --git a/sys/netinet/tcp_subr.c b/sys/netinet/tcp_subr.c
index 1fce7c591639..2e039ebbfdd2 100644
--- a/sys/netinet/tcp_subr.c
+++ b/sys/netinet/tcp_subr.c
@@ -3205,7 +3205,7 @@ tcp6_next_pmtu(const struct icmp6_hdr *icmp6)
* small, set to the min.
*/
if (mtu < IPV6_MMTU)
- mtu = IPV6_MMTU - 8; /* XXXNP: what is the adjustment for? */
+ mtu = IPV6_MMTU;
return (mtu);
}
diff --git a/sys/netinet6/icmp6.c b/sys/netinet6/icmp6.c
index d89515d7eda5..f98381499b2d 100644
--- a/sys/netinet6/icmp6.c
+++ b/sys/netinet6/icmp6.c
@@ -159,6 +159,7 @@ static int ni6_addrs(struct icmp6_nodeinfo *, struct mbuf *,
static int ni6_store_addrs(struct icmp6_nodeinfo *, struct icmp6_nodeinfo *,
struct ifnet *, int);
static int icmp6_notify_error(struct mbuf **, int, int);
+static void icmp6_mtudisc_update(struct ip6ctlparam *ip6cp);
/*
* Kernel module interface for updating icmp6stat. The argument is an index
@@ -1115,7 +1116,7 @@ icmp6_notify_error(struct mbuf **mp, int off, int
icmp6len)
if (icmp6type == ICMP6_PACKET_TOO_BIG) {
notifymtu = ntohl(icmp6->icmp6_mtu);
ip6cp.ip6c_cmdarg = (void *)¬ifymtu;
- icmp6_mtudisc_update(&ip6cp, 1); /*XXX*/
+ icmp6_mtudisc_update(&ip6cp);
}
if (ip6_ctlprotox[nxt] != NULL)
@@ -1130,47 +1131,18 @@ icmp6_notify_error(struct mbuf **mp, int off, int
icmp6len)
return (-1);
}
-void
-icmp6_mtudisc_update(struct ip6ctlparam *ip6cp, int validated)
+static void
+icmp6_mtudisc_update(struct ip6ctlparam *ip6cp)
{
struct in6_addr *dst = &ip6cp->ip6c_finaldst->sin6_addr;
struct icmp6_hdr *icmp6 = ip6cp->ip6c_icmp6;
- struct mbuf *m = ip6cp->ip6c_m; /* will be necessary for scope issue */
+ struct mbuf *m = ip6cp->ip6c_m;
u_int mtu = ntohl(icmp6->icmp6_mtu);
struct in_conninfo inc;
uint32_t max_mtu;
-#if 0
- /*
- * RFC2460 section 5, last paragraph.
- * even though minimum link MTU for IPv6 is IPV6_MMTU,
- * we may see ICMPv6 too big with mtu < IPV6_MMTU
- * due to packet translator in the middle.
- * see ip6_output() and ip6_getpmtu() "alwaysfrag" case for
- * special handling.
- */
if (mtu < IPV6_MMTU)
return;
-#endif
-
- /*
- * we reject ICMPv6 too big with abnormally small value.
- * XXX what is the good definition of "abnormally small"?
- */
- if (mtu < sizeof(struct ip6_hdr) + sizeof(struct ip6_frag) + 8)
- return;
-
- if (!validated)
- return;
-
- /*
- * In case the suggested mtu is less than IPV6_MMTU, we
- * only need to remember that it was for above mentioned
- * "alwaysfrag" case.
- * Try to be as close to the spec as possible.
- */
- if (mtu < IPV6_MMTU)
- mtu = IPV6_MMTU - 8;
bzero(&inc, sizeof(inc));
inc.inc_fibnum = M_GETFIB(m);
diff --git a/sys/netinet6/ip6_output.c b/sys/netinet6/ip6_output.c
index ed71c58fffbe..6299ce6e146b 100644
--- a/sys/netinet6/ip6_output.c
+++ b/sys/netinet6/ip6_output.c
@@ -145,11 +145,10 @@ static int ip6_insertfraghdr(struct mbuf *, struct mbuf
*, int,
struct ip6_frag **);
static int ip6_insert_jumboopt(struct ip6_exthdrs *, u_int32_t);
static int ip6_splithdr(struct mbuf *, struct ip6_exthdrs *);
-static int ip6_getpmtu(struct route_in6 *, int,
- struct ifnet *, const struct in6_addr *, u_long *, int *, u_int,
- u_int);
-static int ip6_calcmtu(struct ifnet *, const struct in6_addr *, u_long,
- u_long *, int *, u_int);
+static void ip6_getpmtu(struct route_in6 *, int,
+ struct ifnet *, const struct in6_addr *, u_long *, u_int, u_int);
+static void ip6_calcmtu(struct ifnet *, const struct in6_addr *, u_long,
+ u_long *, u_int);
static int ip6_getpmtu_ctl(u_int, const struct in6_addr *, u_long *);
static int copypktopts(struct ip6_pktopts *, struct ip6_pktopts *, int);
@@ -418,7 +417,7 @@ ip6_output(struct mbuf *m0, struct ip6_pktopts *opt,
int vlan_pcp = -1;
struct in6_ifaddr *ia = NULL;
u_long mtu;
- int alwaysfrag, dontfrag;
+ int dontfrag;
u_int32_t optlen, plen = 0, unfragpartlen;
struct ip6_exthdrs exthdrs;
struct in6_addr src0, dst0;
@@ -939,12 +938,10 @@ nonh6lookup:
*ifpp = ifp;
/* Determine path MTU. */
- if ((error = ip6_getpmtu(ro_pmtu, ro != ro_pmtu, ifp, &ip6->ip6_dst,
- &mtu, &alwaysfrag, fibnum, *nexthdrp)) != 0)
- goto bad;
- KASSERT(mtu > 0, ("%s:%d: mtu %ld, ro_pmtu %p ro %p ifp %p "
- "alwaysfrag %d fibnum %u\n", __func__, __LINE__, mtu, ro_pmtu, ro,
- ifp, alwaysfrag, fibnum));
+ ip6_getpmtu(ro_pmtu, ro != ro_pmtu, ifp, &ip6->ip6_dst, &mtu, fibnum,
+ *nexthdrp);
+ KASSERT(mtu > 0, ("%s:%d: mtu %ld, ro_pmtu %p ro %p ifp %p fibnum %u",
+ __func__, __LINE__, mtu, ro_pmtu, ro, ifp, fibnum));
/*
* The caller of this function may specify to use the minimum MTU
@@ -1121,20 +1118,13 @@ passout:
* Send the packet to the outgoing interface.
* If necessary, do IPv6 fragmentation before sending.
*
- * The logic here is rather complex:
- * 1: normal case (dontfrag == 0, alwaysfrag == 0)
+ * 1: normal case (dontfrag == 0)
* 1-a: send as is if tlen <= path mtu
* 1-b: fragment if tlen > path mtu
*
* 2: if user asks us not to fragment (dontfrag == 1)
* 2-a: send as is if tlen <= interface mtu
* 2-b: error if tlen > interface mtu
- *
- * 3: if we always need to attach fragment header (alwaysfrag == 1)
- * always fragment
- *
- * 4: if dontfrag == 1 && alwaysfrag == 1
- * error, as we cannot handle this conflicting request.
*/
sw_csum = m->m_pkthdr.csum_flags;
if (!hdrsplit) {
@@ -1157,14 +1147,9 @@ passout:
dontfrag = 1;
else
dontfrag = 0;
- if (dontfrag && alwaysfrag) { /* Case 4. */
- /* Conflicting request - can't transmit. */
- error = EMSGSIZE;
- goto bad;
- }
if (dontfrag && tlen > IN6_LINKMTU(ifp) && !tso) { /* Case 2-b. */
/*
- * Even if the DONTFRAG option is specified, we cannot send the
+ * If the DONTFRAG option is specified, we cannot send the
* packet when the data length is larger than the MTU of the
* outgoing interface.
* Notify the error by sending IPV6_PATHMTU ancillary data if
@@ -1178,7 +1163,7 @@ passout:
}
/* Transmit packet without fragmentation. */
- if (dontfrag || (!alwaysfrag && tlen <= mtu)) { /* Cases 1-a and 2-a. */
+ if (dontfrag || tlen <= mtu) { /* Cases 1-a and 2-a. */
struct in6_ifaddr *ia6;
ip6 = mtod(m, struct ip6_hdr *);
@@ -1194,7 +1179,7 @@ passout:
goto done;
}
- /* Try to fragment the packet. Cases 1-b and 3. */
+ /* Try to fragment the packet. Case 1-b. */
if (mtu < IPV6_MMTU) {
/* Path MTU cannot be less than IPV6_MMTU. */
error = EMSGSIZE;
@@ -1478,9 +1463,10 @@ ip6_getpmtu_ctl(u_int fibnum, const struct in6_addr
*dst, u_long *mtup)
NET_EPOCH_ENTER(et);
nh = fib6_lookup(fibnum, &kdst, scopeid, NHR_NONE, 0);
- if (nh != NULL)
- error = ip6_calcmtu(nh->nh_ifp, dst, nh->nh_mtu, mtup, NULL, 0);
- else
+ if (nh != NULL) {
+ ip6_calcmtu(nh->nh_ifp, dst, nh->nh_mtu, mtup, 0);
+ error = 0;
+ } else
error = EHOSTUNREACH;
NET_EPOCH_EXIT(et);
@@ -1494,13 +1480,12 @@ ip6_getpmtu_ctl(u_int fibnum, const struct in6_addr
*dst, u_long *mtup)
* inside @ro_pmtu to avoid subsequent route lookups after packet
* filter processing.
*
- * Stores mtu and always-frag value into @mtup and @alwaysfragp.
- * Returns 0 on success.
+ * Stores mtu into @mtup.
*/
-static int
+static void
ip6_getpmtu(struct route_in6 *ro_pmtu, int do_lookup,
struct ifnet *ifp, const struct in6_addr *dst, u_long *mtup,
- int *alwaysfragp, u_int fibnum, u_int proto)
+ u_int fibnum, u_int proto)
{
struct nhop_object *nh;
struct in6_addr kdst;
@@ -1544,65 +1529,41 @@ ip6_getpmtu(struct route_in6 *ro_pmtu, int do_lookup,
if (ro_pmtu != NULL && ro_pmtu->ro_nh != NULL)
mtu = ro_pmtu->ro_nh->nh_mtu;
- return (ip6_calcmtu(ifp, dst, mtu, mtup, alwaysfragp, proto));
+ ip6_calcmtu(ifp, dst, mtu, mtup, proto);
}
/*
* Calculate MTU based on transmit @ifp, route mtu @rt_mtu and
* hostcache data for @dst.
- * Stores mtu and always-frag value into @mtup and @alwaysfragp.
- *
- * Returns 0 on success.
+ * Stores mtu into @mtup.
*/
-static int
+static void
ip6_calcmtu(struct ifnet *ifp, const struct in6_addr *dst, u_long rt_mtu,
- u_long *mtup, int *alwaysfragp, u_int proto)
+ u_long *mtup, u_int proto)
{
u_long mtu = 0;
- int alwaysfrag = 0;
- int error = 0;
if (rt_mtu > 0) {
- u_int32_t ifmtu;
- struct in_conninfo inc;
-
- bzero(&inc, sizeof(inc));
- inc.inc_flags |= INC_ISIPV6;
- inc.inc6_faddr = *dst;
-
- ifmtu = IN6_LINKMTU(ifp);
+ /* Skip the hostcache if the protocol handles PMTU changes. */
+ if (proto != IPPROTO_TCP && proto != IPPROTO_SCTP) {
+ struct in_conninfo inc = {
+ .inc_flags = INC_ISIPV6,
+ .inc6_faddr = *dst,
+ };
- /* TCP is known to react to pmtu changes so skip hc */
- if (proto != IPPROTO_TCP)
mtu = tcp_hc_getmtu(&inc);
+ }
if (mtu)
mtu = min(mtu, rt_mtu);
else
mtu = rt_mtu;
- if (mtu == 0)
- mtu = ifmtu;
- else if (mtu < IPV6_MMTU) {
- /*
- * RFC2460 section 5, last paragraph:
- * if we record ICMPv6 too big message with
- * mtu < IPV6_MMTU, transmit packets sized IPV6_MMTU
- * or smaller, with framgent header attached.
- * (fragment header is needed regardless from the
- * packet size, for translators to identify packets)
- */
- alwaysfrag = 1;
- mtu = IPV6_MMTU;
- }
- } else if (ifp) {
+ }
+
+ if (mtu == 0)
mtu = IN6_LINKMTU(ifp);
- } else
- error = EHOSTUNREACH; /* XXX */
*mtup = mtu;
- if (alwaysfragp)
- *alwaysfragp = alwaysfrag;
- return (error);
}
/*
