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Add a limit of the number of fragments per IPv6 packet.

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The IPv4 fragment reassembly code supports a limit on the number of
fragments per packet. The default limit is currently 17 fragments.
Among other things, this limit serves to limit the number of fragments
the code must parse when trying to reassembly a packet.

Add a limit to the IPv6 reassembly code. By default, limit a packet
to 65 fragments (64 on the queue, plus one final fragment to complete
the packet). This allows an average fragment size of 1,008 bytes, which
should be sufficient to hold a fragment. (Recall that the IPv6 minimum
MTU is 1280 bytes. Therefore, this configuration allows a full-size
IPv6 packet to be fragmented on a link with the minimum MTU and still
carry approximately 272 bytes of headers before the fragmented portion
of the packet.)

Users can adjust this limit using the net.inet6.ip6.maxfragsperpacket
sysctl.

Reviewed by:	jhb
Security:	FreeBSD-SA-18:10.ip
Security:	CVE-2018-6923
This commit is contained in:
Jonathan T. Looney 2018-08-14 17:26:07 +00:00
parent 2adfd64f35
commit 03c99d7662
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=337782
4 changed files with 18 additions and 1 deletions
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10
sys/netinet6/frag6.c
View File

@ -136,6 +136,7 @@ frag6_init(void)
mtx_init(&V_ip6q[i].lock, "ip6qlock", NULL, MTX_DEF);
}
V_ip6q_hashseed = arc4random();
V_ip6_maxfragsperpacket = 64;
if (!IS_DEFAULT_VNET(curvnet))
return;
@ -533,6 +534,7 @@ frag6_input(struct mbuf **mp, int *offp, int proto)
/*
* Stick new segment in its place;
* check for complete reassembly.
* If not complete, check fragment limit.
* Move to front of packet queue, as we are
* the most recently active fragmented packet.
*/
@ -549,12 +551,20 @@ frag6_input(struct mbuf **mp, int *offp, int proto)
for (af6 = q6->ip6q_down; af6 != (struct ip6asfrag *)q6;
af6 = af6->ip6af_down) {
if (af6->ip6af_off != next) {
if (q6->ip6q_nfrag > V_ip6_maxfragsperpacket) {
IP6STAT_INC(ip6s_fragdropped);
frag6_freef(q6, hash);
}
IP6Q_UNLOCK(hash);
return IPPROTO_DONE;
}
next += af6->ip6af_frglen;
}
if (af6->ip6af_up->ip6af_mff) {
if (q6->ip6q_nfrag > V_ip6_maxfragsperpacket) {
IP6STAT_INC(ip6s_fragdropped);
frag6_freef(q6, hash);
}
IP6Q_UNLOCK(hash);
return IPPROTO_DONE;
}

3
sys/netinet6/in6.h
View File

@ -642,7 +642,8 @@ struct ip6_mtuinfo {
#define IPV6CTL_INTRQMAXLEN 51 /* max length of IPv6 netisr queue */
#define IPV6CTL_INTRDQMAXLEN 52 /* max length of direct IPv6 netisr
* queue */
#define IPV6CTL_MAXID 53
#define IPV6CTL_MAXFRAGSPERPACKET 53 /* Max fragments per packet */
#define IPV6CTL_MAXID 54
#endif /* __BSD_VISIBLE */
/*

4
sys/netinet6/in6_proto.c
View File

@ -386,6 +386,7 @@ VNET_DEFINE(int, ip6_norbit_raif) = 0;
VNET_DEFINE(int, ip6_rfc6204w3) = 0;
VNET_DEFINE(int, ip6_maxfragpackets); /* initialized in frag6.c:frag6_init() */
int ip6_maxfrags; /* initialized in frag6.c:frag6_init() */
VNET_DEFINE(int, ip6_maxfragsperpacket); /* initialized in frag6.c:frag6_init() */
VNET_DEFINE(int, ip6_log_interval) = 5;
VNET_DEFINE(int, ip6_hdrnestlimit) = 15;/* How many header options will we
* process? */
@ -563,6 +564,9 @@ SYSCTL_INT(_net_inet6_ip6, IPV6CTL_MAXFRAGS, maxfrags,
"Maximum allowed number of outstanding IPv6 packet fragments. "
"A value of 0 means no fragmented packets will be accepted, while a "
"a value of -1 means no limit");
SYSCTL_INT(_net_inet6_ip6, IPV6CTL_MAXFRAGSPERPACKET, maxfragsperpacket,
CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(ip6_maxfragsperpacket), 0,
"Maximum allowed number of fragments per packet");
SYSCTL_INT(_net_inet6_ip6, IPV6CTL_MCAST_PMTU, mcast_pmtu,
CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(ip6_mcast_pmtu), 0,
"Enable path MTU discovery for multicast packets");

2
sys/netinet6/ip6_var.h
View File

@ -303,6 +303,7 @@ VNET_DECLARE(int, ip6_maxfragpackets); /* Maximum packets in reassembly
* queue */
extern int ip6_maxfrags; /* Maximum fragments in reassembly
* queue */
VNET_DECLARE(int, ip6_maxfragsperpacket); /* Maximum fragments per packet */
VNET_DECLARE(int, ip6_accept_rtadv); /* Acts as a host not a router */
VNET_DECLARE(int, ip6_no_radr); /* No defroute from RA */
VNET_DECLARE(int, ip6_norbit_raif); /* Disable R-bit in NA on RA
@ -317,6 +318,7 @@ VNET_DECLARE(int, ip6_dad_count); /* DupAddrDetectionTransmits */
#define V_ip6_mrouter VNET(ip6_mrouter)
#define V_ip6_sendredirects VNET(ip6_sendredirects)
#define V_ip6_maxfragpackets VNET(ip6_maxfragpackets)
#define V_ip6_maxfragsperpacket VNET(ip6_maxfragsperpacket)
#define V_ip6_accept_rtadv VNET(ip6_accept_rtadv)
#define V_ip6_no_radr VNET(ip6_no_radr)
#define V_ip6_norbit_raif VNET(ip6_norbit_raif)