Patch "sctp: fix src address selection if using secondary addresses for ipv6" has been added to the 3.18-stable tree

This is a note to let you know that I've just added the patch titled

sctp: fix src address selection if using secondary addresses for ipv6

to the 3.18-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
sctp-fix-src-address-selection-if-using-secondary-addresses-for-ipv6.patch
and it can be found in the queue-3.18 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Xin Long <[email protected]>
Date: Fri, 12 May 2017 14:39:52 +0800
Subject: sctp: fix src address selection if using secondary addresses for ipv6

From: Xin Long <[email protected]>

[ Upstream commit dbc2b5e9a09e9a6664679a667ff81cff6e5f2641 ]

Commit 0ca50d12fe46 ("sctp: fix src address selection if using secondary addresses") has fixed a src address selection issue when using secondary addresses for ipv4.

Now sctp ipv6 also has the similar issue. When using a secondary address, sctp_v6_get_dst tries to choose the saddr which has the most same bits with the daddr by sctp_v6_addr_match_len. It may make some cases not work as expected.

hostA:
[1] fd21:356b:459a:cf10::11 (eth1)
[2] fd21:356b:459a:cf20::11 (eth2)

hostB:
[a] fd21:356b:459a:cf30::2 (eth1)
[b] fd21:356b:459a:cf40::2 (eth2)

route from hostA to hostB:
fd21:356b:459a:cf30::/64 dev eth1 metric 1024 mtu 1500

The expected path should be:
fd21:356b:459a:cf10::11 <-> fd21:356b:459a:cf30::2
But addr[2] matches addr[a] more bits than addr[1] does, according to sctp_v6_addr_match_len. It causes the path to be:
fd21:356b:459a:cf20::11 <-> fd21:356b:459a:cf30::2

This patch is to fix it with the same way as Marcelo's fix for sctp ipv4. As no ip_dev_find for ipv6, this patch is to use ipv6_chk_addr to check if the saddr is in a dev instead.

Note that for backwards compatibility, it will still do the addr_match_len check here when no optimal is found.

---
 net/sctp/ipv6.c |   46 +++++++++++++++++++++++++++++-----------------
 1 file changed, 29 insertions(+), 17 deletions(-)

@@ -239,12 +239,10 @@ static void sctp_v6_get_dst(struct sctp_
 	struct sctp_bind_addr *bp;
 	struct ipv6_pinfo *np = inet6_sk(sk);
 	struct sctp_sockaddr_entry *laddr;
-	union sctp_addr *baddr = NULL;
 	union sctp_addr *daddr = &t->ipaddr;
 	union sctp_addr dst_saddr;
 	struct in6_addr *final_p, final;
 	__u8 matchlen = 0;
-	__u8 bmatchlen;
 	sctp_scope_t scope;
 
 	memset(fl6, 0, sizeof(struct flowi6));

@@ -311,23 +309,37 @@ static void sctp_v6_get_dst(struct sctp_
 	 */
 	rcu_read_lock();
 	list_for_each_entry_rcu(laddr, &bp->address_list, list) {
-		if (!laddr->valid)
+		struct dst_entry *bdst;
+		__u8 bmatchlen;
+
+		if (!laddr->valid ||
+		    laddr->state != SCTP_ADDR_SRC ||
+		    laddr->a.sa.sa_family != AF_INET6 ||
+		    scope > sctp_scope(&laddr->a))
 			continue;
-		if ((laddr->state == SCTP_ADDR_SRC) &&
-		    (laddr->a.sa.sa_family == AF_INET6) &&
-		    (scope <= sctp_scope(&laddr->a))) {
-			bmatchlen = sctp_v6_addr_match_len(daddr, &laddr->a);
-			if (!baddr || (matchlen < bmatchlen)) {
-				baddr = &laddr->a;
-				matchlen = bmatchlen;
-			}
-		}
-	}
-	if (baddr) {
-		fl6->saddr = baddr->v6.sin6_addr;
-		fl6->fl6_sport = baddr->v6.sin6_port;
+
+		fl6->saddr = laddr->a.v6.sin6_addr;
+		fl6->fl6_sport = laddr->a.v6.sin6_port;
 		final_p = fl6_update_dst(fl6, rcu_dereference(np->opt), &final);
-		dst = ip6_dst_lookup_flow(sk, fl6, final_p);
+		bdst = ip6_dst_lookup_flow(sk, fl6, final_p);
+
+		if (!IS_ERR(bdst) &&
+		    ipv6_chk_addr(dev_net(bdst->dev),
+				  &laddr->a.v6.sin6_addr, bdst->dev, 1)) {
+			if (!IS_ERR_OR_NULL(dst))
+				dst_release(dst);
+			dst = bdst;
+			break;
+		}
+
+		bmatchlen = sctp_v6_addr_match_len(daddr, &laddr->a);
+		if (matchlen > bmatchlen)
+			continue;
+
+		if (!IS_ERR_OR_NULL(dst))
+			dst_release(dst);
+		dst = bdst;
+		matchlen = bmatchlen;
 	}
 	rcu_read_unlock();
 

Patches currently in stable-queue which might be from [email protected] are

queue-3.18/sctp-fix-src-address-selection-if-using-secondary-addresses-for-ipv6.patch queue-3.18/sctp-fix-icmp-processing-if-skb-is-non-linear.patch