ipv6: Move nexthop_find_by_id() after fib6_info_alloc().

We will get rid of RTNL from RTM_NEWROUTE and SIOCADDRT.

Then, we must perform two lookups for nexthop and dev under RCU
to guarantee their lifetime.

ip6_route_info_create() calls nexthop_find_by_id() first if
RTA_NH_ID is specified, and then allocates struct fib6_info.

nexthop_find_by_id() must be called under RCU, but we do not want
to use GFP_ATOMIC for memory allocation here, which will be likely
to fail in ip6_route_multipath_add().

Let's move nexthop_find_by_id() after the memory allocation so
that we can later split ip6_route_info_create() into two parts:
the sleepable part and the RCU part.

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Acked-by: Paolo Abeni <pabeni@redhat.com>
Link: https://patch.msgid.link/20250418000443.43734-6-kuniyu@amazon.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

1 files changed, 18 insertions, 16 deletions

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 88d2f85ed69d..f66f90f8f153 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -3734,24 +3734,11 @@ static struct fib6_info *ip6_route_info_create(struct fib6_config *cfg,
 {
 	struct net *net = cfg->fc_nlinfo.nl_net;
 	struct fib6_info *rt = NULL;
-	struct nexthop *nh = NULL;
 	struct fib6_table *table;
 	struct fib6_nh *fib6_nh;
-	int err = -EINVAL;
+	int err = -ENOBUFS;
 	int addr_type;
 
-	if (cfg->fc_nh_id) {
-		nh = nexthop_find_by_id(net, cfg->fc_nh_id);
-		if (!nh) {
-			NL_SET_ERR_MSG(extack, "Nexthop id does not exist");
-			goto out;
-		}
-		err = fib6_check_nexthop(nh, cfg, extack);
-		if (err)
-			goto out;
-	}
-
-	err = -ENOBUFS;
 	if (cfg->fc_nlinfo.nlh &&
 	    !(cfg->fc_nlinfo.nlh->nlmsg_flags & NLM_F_CREATE)) {
 		table = fib6_get_table(net, cfg->fc_table);
@@ -3767,7 +3754,7 @@ static struct fib6_info *ip6_route_info_create(struct fib6_config *cfg,
 		goto out;
 
 	err = -ENOMEM;
-	rt = fib6_info_alloc(gfp_flags, !nh);
+	rt = fib6_info_alloc(gfp_flags, !cfg->fc_nh_id);
 	if (!rt)
 		goto out;
 
@@ -3803,12 +3790,27 @@ static struct fib6_info *ip6_route_info_create(struct fib6_config *cfg,
 	ipv6_addr_prefix(&rt->fib6_src.addr, &cfg->fc_src, cfg->fc_src_len);
 	rt->fib6_src.plen = cfg->fc_src_len;
 #endif
-	if (nh) {
+
+	if (cfg->fc_nh_id) {
+		struct nexthop *nh;
+
+		nh = nexthop_find_by_id(net, cfg->fc_nh_id);
+		if (!nh) {
+			err = -EINVAL;
+			NL_SET_ERR_MSG(extack, "Nexthop id does not exist");
+			goto out_free;
+		}
+
+		err = fib6_check_nexthop(nh, cfg, extack);
+		if (err)
+			goto out_free;
+
 		if (!nexthop_get(nh)) {
 			NL_SET_ERR_MSG(extack, "Nexthop has been deleted");
 			err = -ENOENT;
 			goto out_free;
 		}
+
 		rt->nh = nh;
 		fib6_nh = nexthop_fib6_nh(rt->nh);
 	} else {