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 9ab4bf704e864358215d2370d33d3d9668681923..ccf171f7eb60d462e0ebf49c9e876016e963ffa5 100644 (file)
--- a/include/net/inet_connection_sock.h
+++ b/include/net/inet_connection_sock.h
@@ -175,6 +175,7 @@ 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 54ca8dcbfb4335d657b5cea323aa7d8c4316d49e..4afb4376c97e811a17124ca53e9946484513a9ac 100644 (file)
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1779,6 +1779,13 @@ 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 459af1f8973958611c43936b0894f6154d23b99a..17eb9ae912239531512f61f0594cf72a5ef49fdf 100644 (file)
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -771,6 +771,20 @@ 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 a4f41859231448b00378fb82219c8a47c33b41f3..5887eac87bd286ec615b6362b9765b95bff51846 100644 (file)
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2930,6 +2930,8 @@ 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);