phonet: no longer hold RTNL in route_dumpit()

route_dumpit() already relies on RCU, RTNL is not needed.

Also change return value at the end of a dump.
This allows NLMSG_DONE to be appended to the current
skb at the end of a dump, saving a couple of recvmsg()
system calls.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Remi Denis-Courmont <courmisch@gmail.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/20240507121748.416287-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/phonet/pn_netlink.c b/net/phonet/pn_netlink.c
index 59aebe29689077bfa77d37516aea4617fe3b8a50..92245fdfa846cb8b9747764a3330e17d8c6b1f16 100644 (file)
--- a/net/phonet/pn_netlink.c
+++ b/net/phonet/pn_netlink.c
@@ -178,7 +178,7 @@ static int fill_route(struct sk_buff *skb, struct net_device *dev, u8 dst,
        rtm->rtm_type = RTN_UNICAST;
        rtm->rtm_flags = 0;
        if (nla_put_u8(skb, RTA_DST, dst) ||
-           nla_put_u32(skb, RTA_OIF, dev->ifindex))
+           nla_put_u32(skb, RTA_OIF, READ_ONCE(dev->ifindex)))
                goto nla_put_failure;
        nlmsg_end(skb, nlh);
        return 0;
@@ -263,6 +263,7 @@ static int route_doit(struct sk_buff *skb, struct nlmsghdr *nlh,
 static int route_dumpit(struct sk_buff *skb, struct netlink_callback *cb)
 {
        struct net *net = sock_net(skb->sk);
+       int err = 0;
        u8 addr;
 
        rcu_read_lock();
@@ -272,16 +273,16 @@ static int route_dumpit(struct sk_buff *skb, struct netlink_callback *cb)
                if (!dev)
                        continue;
 
-               if (fill_route(skb, dev, addr << 2, NETLINK_CB(cb->skb).portid,
-                              cb->nlh->nlmsg_seq, RTM_NEWROUTE) < 0)
-                       goto out;
+               err = fill_route(skb, dev, addr << 2,
+                                NETLINK_CB(cb->skb).portid,
+                                cb->nlh->nlmsg_seq, RTM_NEWROUTE);
+               if (err < 0)
+                       break;
        }
-
-out:
        rcu_read_unlock();
        cb->args[0] = addr;
 
-       return skb->len;
+       return err;
 }
 
 int __init phonet_netlink_register(void)
@@ -301,6 +302,6 @@ int __init phonet_netlink_register(void)
        rtnl_register_module(THIS_MODULE, PF_PHONET, RTM_DELROUTE,
                             route_doit, NULL, 0);
        rtnl_register_module(THIS_MODULE, PF_PHONET, RTM_GETROUTE,
-                            NULL, route_dumpit, 0);
+                            NULL, route_dumpit, RTNL_FLAG_DUMP_UNLOCKED);
        return 0;
 }