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![Linus Lüssing](/assets/img/avatar_default.png)
The IPv6 Multicast Router Advertisements parsing has the following two
issues:
For one thing, ICMPv6 MRD Advertisements are smaller than ICMPv6 MLD
messages (ICMPv6 MRD Adv.: 8 bytes vs. ICMPv6 MLDv1/2: >= 24 bytes,
assuming MLDv2 Reports with at least one multicast address entry).
When ipv6_mc_check_mld_msg() tries to parse an Multicast Router
Advertisement its MLD length check will fail - and it will wrongly
return -EINVAL, even if we have a valid MRD Advertisement. With the
returned -EINVAL the bridge code will assume a broken packet and will
wrongly discard it, potentially leading to multicast packet loss towards
multicast routers.
The second issue is the MRD header parsing in
br_ip6_multicast_mrd_rcv(): It wrongly checks for an ICMPv6 header
immediately after the IPv6 header (IPv6 next header type). However
according to RFC4286, section 2 all MRD messages contain a Router Alert
option (just like MLD). So instead there is an IPv6 Hop-by-Hop option
for the Router Alert between the IPv6 and ICMPv6 header, again leading
to the bridge wrongly discarding Multicast Router Advertisements.
To fix these two issues, introduce a new return value -ENODATA to
ipv6_mc_check_mld() to indicate a valid ICMPv6 packet with a hop-by-hop
option which is not an MLD but potentially an MRD packet. This also
simplifies further parsing in the bridge code, as ipv6_mc_check_mld()
already fully checks the ICMPv6 header and hop-by-hop option.
These issues were found and fixed with the help of the mrdisc tool
(https://github.com/troglobit/mrdisc).
Fixes: 4b3087c7e3
("bridge: Snoop Multicast Router Advertisements")
Signed-off-by: Linus Lüssing <linus.luessing@c0d3.blue>
Signed-off-by: David S. Miller <davem@davemloft.net>
190 lines
4.4 KiB
C
190 lines
4.4 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/* Copyright (C) 2010: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
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* Copyright (C) 2015: Linus Lüssing <linus.luessing@c0d3.blue>
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*
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* Based on the MLD support added to br_multicast.c by YOSHIFUJI Hideaki.
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*/
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#include <linux/skbuff.h>
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#include <net/ipv6.h>
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#include <net/mld.h>
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#include <net/addrconf.h>
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#include <net/ip6_checksum.h>
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static int ipv6_mc_check_ip6hdr(struct sk_buff *skb)
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{
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const struct ipv6hdr *ip6h;
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unsigned int len;
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unsigned int offset = skb_network_offset(skb) + sizeof(*ip6h);
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if (!pskb_may_pull(skb, offset))
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return -EINVAL;
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ip6h = ipv6_hdr(skb);
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if (ip6h->version != 6)
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return -EINVAL;
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len = offset + ntohs(ip6h->payload_len);
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if (skb->len < len || len <= offset)
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return -EINVAL;
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skb_set_transport_header(skb, offset);
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return 0;
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}
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static int ipv6_mc_check_exthdrs(struct sk_buff *skb)
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{
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const struct ipv6hdr *ip6h;
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int offset;
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u8 nexthdr;
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__be16 frag_off;
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ip6h = ipv6_hdr(skb);
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if (ip6h->nexthdr != IPPROTO_HOPOPTS)
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return -ENOMSG;
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nexthdr = ip6h->nexthdr;
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offset = skb_network_offset(skb) + sizeof(*ip6h);
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offset = ipv6_skip_exthdr(skb, offset, &nexthdr, &frag_off);
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if (offset < 0)
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return -EINVAL;
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if (nexthdr != IPPROTO_ICMPV6)
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return -ENOMSG;
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skb_set_transport_header(skb, offset);
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return 0;
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}
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static int ipv6_mc_check_mld_reportv2(struct sk_buff *skb)
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{
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unsigned int len = skb_transport_offset(skb);
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len += sizeof(struct mld2_report);
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return ipv6_mc_may_pull(skb, len) ? 0 : -EINVAL;
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}
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static int ipv6_mc_check_mld_query(struct sk_buff *skb)
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{
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unsigned int transport_len = ipv6_transport_len(skb);
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struct mld_msg *mld;
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unsigned int len;
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/* RFC2710+RFC3810 (MLDv1+MLDv2) require link-local source addresses */
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if (!(ipv6_addr_type(&ipv6_hdr(skb)->saddr) & IPV6_ADDR_LINKLOCAL))
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return -EINVAL;
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/* MLDv1? */
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if (transport_len != sizeof(struct mld_msg)) {
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/* or MLDv2? */
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if (transport_len < sizeof(struct mld2_query))
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return -EINVAL;
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len = skb_transport_offset(skb) + sizeof(struct mld2_query);
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if (!ipv6_mc_may_pull(skb, len))
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return -EINVAL;
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}
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mld = (struct mld_msg *)skb_transport_header(skb);
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/* RFC2710+RFC3810 (MLDv1+MLDv2) require the multicast link layer
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* all-nodes destination address (ff02::1) for general queries
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*/
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if (ipv6_addr_any(&mld->mld_mca) &&
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!ipv6_addr_is_ll_all_nodes(&ipv6_hdr(skb)->daddr))
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return -EINVAL;
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return 0;
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}
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static int ipv6_mc_check_mld_msg(struct sk_buff *skb)
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{
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unsigned int len = skb_transport_offset(skb) + sizeof(struct mld_msg);
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struct mld_msg *mld;
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if (!ipv6_mc_may_pull(skb, len))
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return -ENODATA;
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mld = (struct mld_msg *)skb_transport_header(skb);
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switch (mld->mld_type) {
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case ICMPV6_MGM_REDUCTION:
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case ICMPV6_MGM_REPORT:
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return 0;
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case ICMPV6_MLD2_REPORT:
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return ipv6_mc_check_mld_reportv2(skb);
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case ICMPV6_MGM_QUERY:
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return ipv6_mc_check_mld_query(skb);
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default:
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return -ENODATA;
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}
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}
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static inline __sum16 ipv6_mc_validate_checksum(struct sk_buff *skb)
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{
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return skb_checksum_validate(skb, IPPROTO_ICMPV6, ip6_compute_pseudo);
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}
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static int ipv6_mc_check_icmpv6(struct sk_buff *skb)
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{
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unsigned int len = skb_transport_offset(skb) + sizeof(struct icmp6hdr);
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unsigned int transport_len = ipv6_transport_len(skb);
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struct sk_buff *skb_chk;
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if (!ipv6_mc_may_pull(skb, len))
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return -EINVAL;
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skb_chk = skb_checksum_trimmed(skb, transport_len,
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ipv6_mc_validate_checksum);
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if (!skb_chk)
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return -EINVAL;
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if (skb_chk != skb)
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kfree_skb(skb_chk);
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return 0;
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}
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/**
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* ipv6_mc_check_mld - checks whether this is a sane MLD packet
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* @skb: the skb to validate
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*
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* Checks whether an IPv6 packet is a valid MLD packet. If so sets
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* skb transport header accordingly and returns zero.
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*
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* -EINVAL: A broken packet was detected, i.e. it violates some internet
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* standard
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* -ENOMSG: IP header validation succeeded but it is not an ICMPv6 packet
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* with a hop-by-hop option.
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* -ENODATA: IP+ICMPv6 header with hop-by-hop option validation succeeded
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* but it is not an MLD packet.
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* -ENOMEM: A memory allocation failure happened.
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*
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* Caller needs to set the skb network header and free any returned skb if it
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* differs from the provided skb.
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*/
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int ipv6_mc_check_mld(struct sk_buff *skb)
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{
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int ret;
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ret = ipv6_mc_check_ip6hdr(skb);
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if (ret < 0)
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return ret;
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ret = ipv6_mc_check_exthdrs(skb);
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if (ret < 0)
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return ret;
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ret = ipv6_mc_check_icmpv6(skb);
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if (ret < 0)
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return ret;
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return ipv6_mc_check_mld_msg(skb);
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}
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EXPORT_SYMBOL(ipv6_mc_check_mld);
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