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Subject[PATCH net] net: bridge: mcast: fix broken length + header check for MRDv6 Adv.
Date
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 <linus.luessing@c0d3.blue>
---
include/net/addrconf.h | 1 -
net/bridge/br_multicast.c | 33 ++++++++-------------------------
net/ipv6/mcast_snoop.c | 12 +++++++-----
3 files changed, 15 insertions(+), 31 deletions(-)

diff --git a/include/net/addrconf.h b/include/net/addrconf.h
index 18f783dcd55f..78ea3e332688 100644
--- a/include/net/addrconf.h
+++ b/include/net/addrconf.h
@@ -233,7 +233,6 @@ void ipv6_mc_unmap(struct inet6_dev *idev);
void ipv6_mc_remap(struct inet6_dev *idev);
void ipv6_mc_init_dev(struct inet6_dev *idev);
void ipv6_mc_destroy_dev(struct inet6_dev *idev);
-int ipv6_mc_check_icmpv6(struct sk_buff *skb);
int ipv6_mc_check_mld(struct sk_buff *skb);
void addrconf_dad_failure(struct sk_buff *skb, struct inet6_ifaddr *ifp);

diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
index 9d265447d654..229309d7b4ff 100644
--- a/net/bridge/br_multicast.c
+++ b/net/bridge/br_multicast.c
@@ -3152,25 +3152,14 @@ static int br_multicast_ipv4_rcv(struct net_bridge *br,
}

#if IS_ENABLED(CONFIG_IPV6)
-static int br_ip6_multicast_mrd_rcv(struct net_bridge *br,
- struct net_bridge_port *port,
- struct sk_buff *skb)
+static void br_ip6_multicast_mrd_rcv(struct net_bridge *br,
+ struct net_bridge_port *port,
+ struct sk_buff *skb)
{
- int ret;
-
- if (ipv6_hdr(skb)->nexthdr != IPPROTO_ICMPV6)
- return -ENOMSG;
-
- ret = ipv6_mc_check_icmpv6(skb);
- if (ret < 0)
- return ret;
-
if (icmp6_hdr(skb)->icmp6_type != ICMPV6_MRDISC_ADV)
- return -ENOMSG;
+ return;

br_multicast_mark_router(br, port);
-
- return 0;
}

static int br_multicast_ipv6_rcv(struct net_bridge *br,
@@ -3184,18 +3173,12 @@ static int br_multicast_ipv6_rcv(struct net_bridge *br,

err = ipv6_mc_check_mld(skb);

- if (err == -ENOMSG) {
+ if (err == -ENOMSG || err == -ENODATA) {
if (!ipv6_addr_is_ll_all_nodes(&ipv6_hdr(skb)->daddr))
BR_INPUT_SKB_CB(skb)->mrouters_only = 1;
-
- if (ipv6_addr_is_all_snoopers(&ipv6_hdr(skb)->daddr)) {
- err = br_ip6_multicast_mrd_rcv(br, port, skb);
-
- if (err < 0 && err != -ENOMSG) {
- br_multicast_err_count(br, port, skb->protocol);
- return err;
- }
- }
+ if (err == -ENODATA &&
+ ipv6_addr_is_all_snoopers(&ipv6_hdr(skb)->daddr))
+ br_ip6_multicast_mrd_rcv(br, port, skb);

return 0;
} else if (err < 0) {
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
--
2.31.0
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