net: better track kernel sockets lifetime

[ Upstream commit 5c70eb5c593d64d93b178905da215a9fd288a4b5 ]

While kernel sockets are dismantled during pernet_operations->exit(),
their freeing can be delayed by any tx packets still held in qdisc
or device queues, due to skb_set_owner_w() prior calls.

This then trigger the following warning from ref_tracker_dir_exit() [1]

To fix this, make sure that kernel sockets own a reference on net->passive.

Add sk_net_refcnt_upgrade() helper, used whenever a kernel socket
is converted to a refcounted one.

[1]

[  136.263918][   T35] ref_tracker: net notrefcnt@ffff8880638f01e0 has 1/2 users at
[  136.263918][   T35]      sk_alloc+0x2b3/0x370
[  136.263918][   T35]      inet6_create+0x6ce/0x10f0
[  136.263918][   T35]      __sock_create+0x4c0/0xa30
[  136.263918][   T35]      inet_ctl_sock_create+0xc2/0x250
[  136.263918][   T35]      igmp6_net_init+0x39/0x390
[  136.263918][   T35]      ops_init+0x31e/0x590
[  136.263918][   T35]      setup_net+0x287/0x9e0
[  136.263918][   T35]      copy_net_ns+0x33f/0x570
[  136.263918][   T35]      create_new_namespaces+0x425/0x7b0
[  136.263918][   T35]      unshare_nsproxy_namespaces+0x124/0x180
[  136.263918][   T35]      ksys_unshare+0x57d/0xa70
[  136.263918][   T35]      __x64_sys_unshare+0x38/0x40
[  136.263918][   T35]      do_syscall_64+0xf3/0x230
[  136.263918][   T35]      entry_SYSCALL_64_after_hwframe+0x77/0x7f
[  136.263918][   T35]
[  136.343488][   T35] ref_tracker: net notrefcnt@ffff8880638f01e0 has 1/2 users at
[  136.343488][   T35]      sk_alloc+0x2b3/0x370
[  136.343488][   T35]      inet6_create+0x6ce/0x10f0
[  136.343488][   T35]      __sock_create+0x4c0/0xa30
[  136.343488][   T35]      inet_ctl_sock_create+0xc2/0x250
[  136.343488][   T35]      ndisc_net_init+0xa7/0x2b0
[  136.343488][   T35]      ops_init+0x31e/0x590
[  136.343488][   T35]      setup_net+0x287/0x9e0
[  136.343488][   T35]      copy_net_ns+0x33f/0x570
[  136.343488][   T35]      create_new_namespaces+0x425/0x7b0
[  136.343488][   T35]      unshare_nsproxy_namespaces+0x124/0x180
[  136.343488][   T35]      ksys_unshare+0x57d/0xa70
[  136.343488][   T35]      __x64_sys_unshare+0x38/0x40
[  136.343488][   T35]      do_syscall_64+0xf3/0x230
[  136.343488][   T35]      entry_SYSCALL_64_after_hwframe+0x77/0x7f

Fixes: 0cafd77dcd03 ("net: add a refcount tracker for kernel sockets")
Reported-by: syzbot+30a19e01a97420719891@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/netdev/67b72aeb.050a0220.14d86d.0283.GAE@google.com/T/#u
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20250220131854.4048077-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

1 files changed, 22 insertions, 5 deletions

diff --git a/net/core/sock.c b/net/core/sock.c
index be84885f9290..9d5dd99cc581 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -2233,6 +2233,7 @@ struct sock *sk_alloc(struct net *net, int family, gfp_t priority,
 			get_net_track(net, &sk->ns_tracker, priority);
 			sock_inuse_add(net, 1);
 		} else {
+			net_passive_inc(net);
 			__netns_tracker_alloc(net, &sk->ns_tracker,
 					      false, priority);
 		}
@@ -2257,6 +2258,7 @@ EXPORT_SYMBOL(sk_alloc);
 static void __sk_destruct(struct rcu_head *head)
 {
 	struct sock *sk = container_of(head, struct sock, sk_rcu);
+	struct net *net = sock_net(sk);
 	struct sk_filter *filter;
 
 	if (sk->sk_destruct)
@@ -2288,14 +2290,28 @@ static void __sk_destruct(struct rcu_head *head)
 	put_cred(sk->sk_peer_cred);
 	put_pid(sk->sk_peer_pid);
 
-	if (likely(sk->sk_net_refcnt))
-		put_net_track(sock_net(sk), &sk->ns_tracker);
-	else
-		__netns_tracker_free(sock_net(sk), &sk->ns_tracker, false);
-
+	if (likely(sk->sk_net_refcnt)) {
+		put_net_track(net, &sk->ns_tracker);
+	} else {
+		__netns_tracker_free(net, &sk->ns_tracker, false);
+		net_passive_dec(net);
+	}
 	sk_prot_free(sk->sk_prot_creator, sk);
 }
 
+void sk_net_refcnt_upgrade(struct sock *sk)
+{
+	struct net *net = sock_net(sk);
+
+	WARN_ON_ONCE(sk->sk_net_refcnt);
+	__netns_tracker_free(net, &sk->ns_tracker, false);
+	net_passive_dec(net);
+	sk->sk_net_refcnt = 1;
+	get_net_track(net, &sk->ns_tracker, GFP_KERNEL);
+	sock_inuse_add(net, 1);
+}
+EXPORT_SYMBOL_GPL(sk_net_refcnt_upgrade);
+
 void sk_destruct(struct sock *sk)
 {
 	bool use_call_rcu = sock_flag(sk, SOCK_RCU_FREE);
@@ -2392,6 +2408,7 @@ struct sock *sk_clone_lock(const struct sock *sk, const gfp_t priority)
 		 * is not properly dismantling its kernel sockets at netns
 		 * destroy time.
 		 */
+		net_passive_inc(sock_net(newsk));
 		__netns_tracker_alloc(sock_net(newsk), &newsk->ns_tracker,
 				      false, priority);
 	}