tcp: properly terminate timers for kernel sockets

[ Upstream commit 151c9c724d05d5b0dd8acd3e11cb69ef1f2dbada ]

We had various syzbot reports about tcp timers firing after
the corresponding netns has been dismantled.

Fortunately Josef Bacik could trigger the issue more often,
and could test a patch I wrote two years ago.

When TCP sockets are closed, we call inet_csk_clear_xmit_timers()
to 'stop' the timers.

inet_csk_clear_xmit_timers() can be called from any context,
including when socket lock is held.
This is the reason it uses sk_stop_timer(), aka del_timer().
This means that ongoing timers might finish much later.

For user sockets, this is fine because each running timer
holds a reference on the socket, and the user socket holds
a reference on the netns.

For kernel sockets, we risk that the netns is freed before
timer can complete, because kernel sockets do not hold
reference on the netns.

This patch adds inet_csk_clear_xmit_timers_sync() function
that using sk_stop_timer_sync() to make sure all timers
are terminated before the kernel socket is released.
Modules using kernel sockets close them in their netns exit()
handler.

Also add sock_not_owned_by_me() helper to get LOCKDEP
support : inet_csk_clear_xmit_timers_sync() must not be called
while socket lock is held.

It is very possible we can revert in the future commit
3a58f13a881e ("net: rds: acquire refcount on TCP sockets")
which attempted to solve the issue in rds only.
(net/smc/af_smc.c and net/mptcp/subflow.c have similar code)

We probably can remove the check_net() tests from
tcp_out_of_resources() and __tcp_close() in the future.

Reported-by: Josef Bacik <josef@toxicpanda.com>
Closes: https://lore.kernel.org/netdev/20240314210740.GA2823176@perftesting/
Fixes: 26abe14379f8 ("net: Modify sk_alloc to not reference count the netns of kernel sockets.")
Fixes: 8a68173691f0 ("net: sk_clone_lock() should only do get_net() if the parent is not a kernel socket")
Link: https://lore.kernel.org/bpf/CANn89i+484ffqb93aQm1N-tjxxvb3WDKX0EbD7318RwRgsatjw@mail.gmail.com/
Signed-off-by: Eric Dumazet <edumazet@google.com>
Tested-by: Josef Bacik <josef@toxicpanda.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Link: https://lore.kernel.org/r/20240322135732.1535772-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/include/net/inet_connection_sock.h b/include/net/inet_connection_sock.h
index 798aad21694e203637e6fb7250e8ef588a3b4de1..b6b7e210f9d7a1663ef61264e21d5a71dbcc1c3f 100644 (file)
--- a/include/net/inet_connection_sock.h
+++ b/include/net/inet_connection_sock.h
@@ -169,6 +169,7 @@ void inet_csk_init_xmit_timers(struct sock *sk,
                               void (*delack_handler)(struct timer_list *),
                               void (*keepalive_handler)(struct timer_list *));
 void inet_csk_clear_xmit_timers(struct sock *sk);
+void inet_csk_clear_xmit_timers_sync(struct sock *sk);
 
 static inline void inet_csk_schedule_ack(struct sock *sk)
 {

diff --git a/include/net/sock.h b/include/net/sock.h
index e19eebaf59f73b6c67e48de3a79577a070ee0cf0..44ebec3fdda6407345521fc3b024af41bbae6ba6 100644 (file)
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1751,6 +1751,13 @@ static inline void sock_owned_by_me(const struct sock *sk)
 #endif
 }
 
+static inline void sock_not_owned_by_me(const struct sock *sk)
+{
+#ifdef CONFIG_LOCKDEP
+       WARN_ON_ONCE(lockdep_sock_is_held(sk) && debug_locks);
+#endif
+}
+
 static inline bool sock_owned_by_user(const struct sock *sk)
 {
        sock_owned_by_me(sk);

diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index da43957a584389547e6ac2f18aae35b620e64db4..27975a44d1f9d3c78e58fd152b9b8e1aaf14dccc 100644 (file)
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -589,6 +589,20 @@ void inet_csk_clear_xmit_timers(struct sock *sk)
 }
 EXPORT_SYMBOL(inet_csk_clear_xmit_timers);
 
+void inet_csk_clear_xmit_timers_sync(struct sock *sk)
+{
+       struct inet_connection_sock *icsk = inet_csk(sk);
+
+       /* ongoing timer handlers need to acquire socket lock. */
+       sock_not_owned_by_me(sk);
+
+       icsk->icsk_pending = icsk->icsk_ack.pending = 0;
+
+       sk_stop_timer_sync(sk, &icsk->icsk_retransmit_timer);
+       sk_stop_timer_sync(sk, &icsk->icsk_delack_timer);
+       sk_stop_timer_sync(sk, &sk->sk_timer);
+}
+
 void inet_csk_delete_keepalive_timer(struct sock *sk)
 {
        sk_stop_timer(sk, &sk->sk_timer);

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 521c15962c7194890ffa4d387be420d3ba504a9b..16fd3da68e9f6fa24d3e947dc0072fa3ca6fd25c 100644 (file)
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2916,6 +2916,8 @@ void tcp_close(struct sock *sk, long timeout)
        lock_sock(sk);
        __tcp_close(sk, timeout);
        release_sock(sk);
+       if (!sk->sk_net_refcnt)
+               inet_csk_clear_xmit_timers_sync(sk);
        sock_put(sk);
 }
 EXPORT_SYMBOL(tcp_close);