From 99014088156cd78867d19514a0bc771c4b86b93b Mon Sep 17 00:00:00 2001 From: Linus Lüssing Date: Sun, 25 Apr 2021 17:27:35 +0200 Subject: net: bridge: mcast: fix broken length + header check for MRDv6 Adv. MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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: 4b3087c7e37f ("bridge: Snoop Multicast Router Advertisements") Signed-off-by: Linus Lüssing Signed-off-by: David S. Miller --- net/ipv6/mcast_snoop.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) (limited to 'net/ipv6/mcast_snoop.c') diff --git a/net/ipv6/mcast_snoop.c b/net/ipv6/mcast_snoop.c index d3d6b6a66e5f..04d5fcdfa6e0 100644 --- a/net/ipv6/mcast_snoop.c +++ b/net/ipv6/mcast_snoop.c @@ -109,7 +109,7 @@ static int ipv6_mc_check_mld_msg(struct sk_buff *skb) struct mld_msg *mld; if (!ipv6_mc_may_pull(skb, len)) - return -EINVAL; + return -ENODATA; mld = (struct mld_msg *)skb_transport_header(skb); @@ -122,7 +122,7 @@ static int ipv6_mc_check_mld_msg(struct sk_buff *skb) case ICMPV6_MGM_QUERY: return ipv6_mc_check_mld_query(skb); default: - return -ENOMSG; + return -ENODATA; } } @@ -131,7 +131,7 @@ static inline __sum16 ipv6_mc_validate_checksum(struct sk_buff *skb) return skb_checksum_validate(skb, IPPROTO_ICMPV6, ip6_compute_pseudo); } -int ipv6_mc_check_icmpv6(struct sk_buff *skb) +static int ipv6_mc_check_icmpv6(struct sk_buff *skb) { unsigned int len = skb_transport_offset(skb) + sizeof(struct icmp6hdr); unsigned int transport_len = ipv6_transport_len(skb); @@ -150,7 +150,6 @@ int ipv6_mc_check_icmpv6(struct sk_buff *skb) return 0; } -EXPORT_SYMBOL(ipv6_mc_check_icmpv6); /** * ipv6_mc_check_mld - checks whether this is a sane MLD packet @@ -161,7 +160,10 @@ EXPORT_SYMBOL(ipv6_mc_check_icmpv6); * * -EINVAL: A broken packet was detected, i.e. it violates some internet * standard - * -ENOMSG: IP header validation succeeded but it is not an MLD packet. + * -ENOMSG: IP header validation succeeded but it is not an ICMPv6 packet + * with a hop-by-hop option. + * -ENODATA: IP+ICMPv6 header with hop-by-hop option validation succeeded + * but it is not an MLD packet. * -ENOMEM: A memory allocation failure happened. * * Caller needs to set the skb network header and free any returned skb if it -- cgit