Patch "ip6mr: fix tables suspicious RCU usage" has been added to the 6.1-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

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

    ip6mr: fix tables suspicious RCU usage

to the 6.1-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:
     ip6mr-fix-tables-suspicious-rcu-usage.patch
and it can be found in the queue-6.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 462f99142cd8da870a1b23a7cd2cdf14e56a0d87
Author: Paolo Abeni <pabeni@xxxxxxxxxx>
Date:   Sun Nov 24 16:40:57 2024 +0100

    ip6mr: fix tables suspicious RCU usage
    
    [ Upstream commit f1553c9894b4dbeb10a2ab15ab1aa113b3b4047c ]
    
    Several places call ip6mr_get_table() with no RCU nor RTNL lock.
    Add RCU protection inside such helper and provide a lockless variant
    for the few callers that already acquired the relevant lock.
    
    Note that some users additionally reference the table outside the RCU
    lock. That is actually safe as the table deletion can happen only
    after all table accesses are completed.
    
    Fixes: e2d57766e674 ("net: Provide compat support for SIOCGETMIFCNT_IN6 and SIOCGETSGCNT_IN6.")
    Fixes: d7c31cbde4bc ("net: ip6mr: add RTM_GETROUTE netlink op")
    Reviewed-by: David Ahern <dsahern@xxxxxxxxxx>
    Signed-off-by: Paolo Abeni <pabeni@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/ipv6/ip6mr.c b/net/ipv6/ip6mr.c
index 27fb5479988af..138f6aee70afc 100644
--- a/net/ipv6/ip6mr.c
+++ b/net/ipv6/ip6mr.c
@@ -125,7 +125,7 @@ static struct mr_table *ip6mr_mr_table_iter(struct net *net,
 	return ret;
 }
 
-static struct mr_table *ip6mr_get_table(struct net *net, u32 id)
+static struct mr_table *__ip6mr_get_table(struct net *net, u32 id)
 {
 	struct mr_table *mrt;
 
@@ -136,6 +136,16 @@ static struct mr_table *ip6mr_get_table(struct net *net, u32 id)
 	return NULL;
 }
 
+static struct mr_table *ip6mr_get_table(struct net *net, u32 id)
+{
+	struct mr_table *mrt;
+
+	rcu_read_lock();
+	mrt = __ip6mr_get_table(net, id);
+	rcu_read_unlock();
+	return mrt;
+}
+
 static int ip6mr_fib_lookup(struct net *net, struct flowi6 *flp6,
 			    struct mr_table **mrt)
 {
@@ -177,7 +187,7 @@ static int ip6mr_rule_action(struct fib_rule *rule, struct flowi *flp,
 
 	arg->table = fib_rule_get_table(rule, arg);
 
-	mrt = ip6mr_get_table(rule->fr_net, arg->table);
+	mrt = __ip6mr_get_table(rule->fr_net, arg->table);
 	if (!mrt)
 		return -EAGAIN;
 	res->mrt = mrt;
@@ -304,6 +314,8 @@ static struct mr_table *ip6mr_get_table(struct net *net, u32 id)
 	return net->ipv6.mrt6;
 }
 
+#define __ip6mr_get_table ip6mr_get_table
+
 static int ip6mr_fib_lookup(struct net *net, struct flowi6 *flp6,
 			    struct mr_table **mrt)
 {
@@ -382,7 +394,7 @@ static struct mr_table *ip6mr_new_table(struct net *net, u32 id)
 {
 	struct mr_table *mrt;
 
-	mrt = ip6mr_get_table(net, id);
+	mrt = __ip6mr_get_table(net, id);
 	if (mrt)
 		return mrt;
 
@@ -411,13 +423,15 @@ static void *ip6mr_vif_seq_start(struct seq_file *seq, loff_t *pos)
 	struct net *net = seq_file_net(seq);
 	struct mr_table *mrt;
 
-	mrt = ip6mr_get_table(net, RT6_TABLE_DFLT);
-	if (!mrt)
+	rcu_read_lock();
+	mrt = __ip6mr_get_table(net, RT6_TABLE_DFLT);
+	if (!mrt) {
+		rcu_read_unlock();
 		return ERR_PTR(-ENOENT);
+	}
 
 	iter->mrt = mrt;
 
-	rcu_read_lock();
 	return mr_vif_seq_start(seq, pos);
 }
 
@@ -2288,11 +2302,13 @@ int ip6mr_get_route(struct net *net, struct sk_buff *skb, struct rtmsg *rtm,
 	struct mfc6_cache *cache;
 	struct rt6_info *rt = (struct rt6_info *)skb_dst(skb);
 
-	mrt = ip6mr_get_table(net, RT6_TABLE_DFLT);
-	if (!mrt)
+	rcu_read_lock();
+	mrt = __ip6mr_get_table(net, RT6_TABLE_DFLT);
+	if (!mrt) {
+		rcu_read_unlock();
 		return -ENOENT;
+	}
 
-	rcu_read_lock();
 	cache = ip6mr_cache_find(mrt, &rt->rt6i_src.addr, &rt->rt6i_dst.addr);
 	if (!cache && skb->dev) {
 		int vif = ip6mr_find_vif(mrt, skb->dev);
@@ -2573,7 +2589,7 @@ static int ip6mr_rtm_getroute(struct sk_buff *in_skb, struct nlmsghdr *nlh,
 		grp = nla_get_in6_addr(tb[RTA_DST]);
 	tableid = tb[RTA_TABLE] ? nla_get_u32(tb[RTA_TABLE]) : 0;
 
-	mrt = ip6mr_get_table(net, tableid ?: RT_TABLE_DEFAULT);
+	mrt = __ip6mr_get_table(net, tableid ?: RT_TABLE_DEFAULT);
 	if (!mrt) {
 		NL_SET_ERR_MSG_MOD(extack, "MR table does not exist");
 		return -ENOENT;
@@ -2618,7 +2634,7 @@ static int ip6mr_rtm_dumproute(struct sk_buff *skb, struct netlink_callback *cb)
 	if (filter.table_id) {
 		struct mr_table *mrt;
 
-		mrt = ip6mr_get_table(sock_net(skb->sk), filter.table_id);
+		mrt = __ip6mr_get_table(sock_net(skb->sk), filter.table_id);
 		if (!mrt) {
 			if (rtnl_msg_family(cb->nlh) != RTNL_FAMILY_IP6MR)
 				return skb->len;