ipv6: remove RTNL protection from inet6_dump_fib()

No longer hold RTNL while calling inet6_dump_fib().

Also change return value for a completed dump,
so that NLMSG_DONE can be appended to current skb,
saving one recvmsg() system call.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/r/20240329183053.644630-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
index 5c558dc..284002a 100644 (file)
--- a/net/ipv6/ip6_fib.c
+++ b/net/ipv6/ip6_fib.c
@@ -623,23 +623,22 @@ static int inet6_dump_fib(struct sk_buff *skb, struct netlink_callback *cb)
        struct rt6_rtnl_dump_arg arg = {
                .filter.dump_exceptions = true,
                .filter.dump_routes = true,
-               .filter.rtnl_held = true,
+               .filter.rtnl_held = false,
        };
        const struct nlmsghdr *nlh = cb->nlh;
        struct net *net = sock_net(skb->sk);
-       unsigned int h, s_h;
        unsigned int e = 0, s_e;
+       struct hlist_head *head;
        struct fib6_walker *w;
        struct fib6_table *tb;
-       struct hlist_head *head;
-       int res = 0;
+       unsigned int h, s_h;
+       int err = 0;
 
+       rcu_read_lock();
        if (cb->strict_check) {
-               int err;
-
                err = ip_valid_fib_dump_req(net, nlh, &arg.filter, cb);
                if (err < 0)
-                       return err;
+                       goto unlock;
        } else if (nlmsg_len(nlh) >= sizeof(struct rtmsg)) {
                struct rtmsg *rtm = nlmsg_data(nlh);
 
@@ -660,8 +659,10 @@ static int inet6_dump_fib(struct sk_buff *skb, struct netlink_callback *cb)
                 * 2. allocate and initialize walker.
                 */
                w = kzalloc(sizeof(*w), GFP_ATOMIC);
-               if (!w)
-                       return -ENOMEM;
+               if (!w) {
+                       err = -ENOMEM;
+                       goto unlock;
+               }
                w->func = fib6_dump_node;
                cb->args[2] = (long)w;
        }
@@ -675,46 +676,46 @@ static int inet6_dump_fib(struct sk_buff *skb, struct netlink_callback *cb)
                tb = fib6_get_table(net, arg.filter.table_id);
                if (!tb) {
                        if (rtnl_msg_family(cb->nlh) != PF_INET6)
-                               goto out;
+                               goto unlock;
 
                        NL_SET_ERR_MSG_MOD(cb->extack, "FIB table does not exist");
-                       return -ENOENT;
+                       err = -ENOENT;
+                       goto unlock;
                }
 
                if (!cb->args[0]) {
-                       res = fib6_dump_table(tb, skb, cb);
-                       if (!res)
+                       err = fib6_dump_table(tb, skb, cb);
+                       if (!err)
                                cb->args[0] = 1;
                }
-               goto out;
+               goto unlock;
        }
 
        s_h = cb->args[0];
        s_e = cb->args[1];
 
-       rcu_read_lock();
        for (h = s_h; h < FIB6_TABLE_HASHSZ; h++, s_e = 0) {
                e = 0;
                head = &net->ipv6.fib_table_hash[h];
                hlist_for_each_entry_rcu(tb, head, tb6_hlist) {
                        if (e < s_e)
                                goto next;
-                       res = fib6_dump_table(tb, skb, cb);
-                       if (res != 0)
-                               goto out_unlock;
+                       err = fib6_dump_table(tb, skb, cb);
+                       if (err != 0)
+                               goto out;
 next:
                        e++;
                }
        }
-out_unlock:
-       rcu_read_unlock();
+out:
        cb->args[1] = e;
        cb->args[0] = h;
-out:
-       res = res < 0 ? res : skb->len;
-       if (res <= 0)
+
+unlock:
+       rcu_read_unlock();
+       if (err <= 0)
                fib6_dump_end(cb);
-       return res;
+       return err;
 }
 
 void fib6_metric_set(struct fib6_info *f6i, int metric, u32 val)
@@ -2506,7 +2507,7 @@ int __init fib6_init(void)
                goto out_kmem_cache_create;
 
        ret = rtnl_register_module(THIS_MODULE, PF_INET6, RTM_GETROUTE, NULL,
-                                  inet6_dump_fib, 0);
+                                  inet6_dump_fib, RTNL_FLAG_DUMP_UNLOCKED);
        if (ret)
                goto out_unregister_subsys;