mpls: Convert mpls_dump_routes() to RCU.

mpls_dump_routes() sets fib_dump_filter.rtnl_held to true and
calls __dev_get_by_index() in mpls_valid_fib_dump_req().

This is the only RTNL dependant in mpls_dump_routes().

Also, synchronize_rcu() in resize_platform_label_table()
guarantees that net->mpls.platform_label is alive under RCU.

Let's convert mpls_dump_routes() to RCU and use dev_get_by_index_rcu().

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Guillaume Nault <gnault@redhat.com>
Link: https://patch.msgid.link/20251029173344.2934622-11-kuniyu@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/mpls/af_mpls.c b/net/mpls/af_mpls.c
index 35ae3dbd7bdc79d6fb67061b2508f2ba71df8b23..f00f75c137dc4703967175740657b2d591f2f572 100644 (file)
--- a/net/mpls/af_mpls.c
+++ b/net/mpls/af_mpls.c
@@ -2153,7 +2153,7 @@ static int mpls_valid_fib_dump_req(struct net *net, const struct nlmsghdr *nlh,
 
                if (i == RTA_OIF) {
                        ifindex = nla_get_u32(tb[i]);
-                       filter->dev = __dev_get_by_index(net, ifindex);
+                       filter->dev = dev_get_by_index_rcu(net, ifindex);
                        if (!filter->dev)
                                return -ENODEV;
                        filter->filter_set = 1;
@@ -2191,20 +2191,19 @@ static int mpls_dump_routes(struct sk_buff *skb, struct netlink_callback *cb)
        struct net *net = sock_net(skb->sk);
        struct mpls_route __rcu **platform_label;
        struct fib_dump_filter filter = {
-               .rtnl_held = true,
+               .rtnl_held = false,
        };
        unsigned int flags = NLM_F_MULTI;
        size_t platform_labels;
        unsigned int index;
+       int err;
 
-       ASSERT_RTNL();
+       rcu_read_lock();
 
        if (cb->strict_check) {
-               int err;
-
                err = mpls_valid_fib_dump_req(net, nlh, &filter, cb);
                if (err < 0)
-                       return err;
+                       goto err;
 
                /* for MPLS, there is only 1 table with fixed type and flags.
                 * If either are set in the filter then return nothing.
@@ -2212,14 +2211,14 @@ static int mpls_dump_routes(struct sk_buff *skb, struct netlink_callback *cb)
                if ((filter.table_id && filter.table_id != RT_TABLE_MAIN) ||
                    (filter.rt_type && filter.rt_type != RTN_UNICAST) ||
                     filter.flags)
-                       return skb->len;
+                       goto unlock;
        }
 
        index = cb->args[0];
        if (index < MPLS_LABEL_FIRST_UNRESERVED)
                index = MPLS_LABEL_FIRST_UNRESERVED;
 
-       platform_label = rtnl_dereference(net->mpls.platform_label);
+       platform_label = rcu_dereference(net->mpls.platform_label);
        platform_labels = net->mpls.platform_labels;
 
        if (filter.filter_set)
@@ -2228,7 +2227,7 @@ static int mpls_dump_routes(struct sk_buff *skb, struct netlink_callback *cb)
        for (; index < platform_labels; index++) {
                struct mpls_route *rt;
 
-               rt = rtnl_dereference(platform_label[index]);
+               rt = rcu_dereference(platform_label[index]);
                if (!rt)
                        continue;
 
@@ -2243,7 +2242,13 @@ static int mpls_dump_routes(struct sk_buff *skb, struct netlink_callback *cb)
        }
        cb->args[0] = index;
 
+unlock:
+       rcu_read_unlock();
        return skb->len;
+
+err:
+       rcu_read_unlock();
+       return err;
 }
 
 static inline size_t lfib_nlmsg_size(struct mpls_route *rt)
@@ -2767,7 +2772,8 @@ static struct rtnl_af_ops mpls_af_ops __read_mostly = {
 static const struct rtnl_msg_handler mpls_rtnl_msg_handlers[] __initdata_or_module = {
        {THIS_MODULE, PF_MPLS, RTM_NEWROUTE, mpls_rtm_newroute, NULL, 0},
        {THIS_MODULE, PF_MPLS, RTM_DELROUTE, mpls_rtm_delroute, NULL, 0},
-       {THIS_MODULE, PF_MPLS, RTM_GETROUTE, mpls_getroute, mpls_dump_routes, 0},
+       {THIS_MODULE, PF_MPLS, RTM_GETROUTE, mpls_getroute, mpls_dump_routes,
+        RTNL_FLAG_DUMP_UNLOCKED},
        {THIS_MODULE, PF_MPLS, RTM_GETNETCONF,
         mpls_netconf_get_devconf, mpls_netconf_dump_devconf,
         RTNL_FLAG_DUMP_UNLOCKED},