linux-kernel - [PATCH net] net/tcp: Disable TCP-AO static key after RCU grace period

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Message-Id: <20240725-tcp-ao-static-branch-rcu-v1-1-021d009beebf@gmail.com>
Date: Thu, 25 Jul 2024 06:00:02 +0100
From: Dmitry Safonov via B4 Relay <devnull+0x7f454c46.gmail.com@...nel.org>
To: Eric Dumazet <edumazet@...gle.com>, 
 "David S. Miller" <davem@...emloft.net>, David Ahern <dsahern@...nel.org>, 
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org, stable@...nel.org, 
 Dmitry Safonov <0x7f454c46@...il.com>
Subject: [PATCH net] net/tcp: Disable TCP-AO static key after RCU grace
 period

From: Dmitry Safonov <0x7f454c46@...il.com>

The lifetime of TCP-AO static_key is the same as the last
tcp_ao_info. On the socket destruction tcp_ao_info ceases to be
with RCU grace period, while tcp-ao static branch is currently deferred
destructed. The static key definition is
: DEFINE_STATIC_KEY_DEFERRED_FALSE(tcp_ao_needed, HZ);

which means that if RCU grace period is delayed by more than a second
and tcp_ao_needed is in the process of disablement, other CPUs may
yet see tcp_ao_info which atent dead, but soon-to-be.
And that breaks the assumption of static_key_fast_inc_not_disabled().

Happened on netdev test-bot[1], so not a theoretical issue:

[] jump_label: Fatal kernel bug, unexpected op at tcp_inbound_hash+0x1a7/0x870 [ffffffffa8c4e9b7] (eb 50 0f 1f 44 != 66 90 0f 1f 00)) size:2 type:1
[] ------------[ cut here ]------------
[] kernel BUG at arch/x86/kernel/jump_label.c:73!
[] Oops: invalid opcode: 0000 [#1] PREEMPT SMP KASAN NOPTI
[] CPU: 3 PID: 243 Comm: kworker/3:3 Not tainted 6.10.0-virtme #1
[] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[] Workqueue: events jump_label_update_timeout
[] RIP: 0010:__jump_label_patch+0x2f6/0x350
...
[] Call Trace:
[]  <TASK>
[]  arch_jump_label_transform_queue+0x6c/0x110
[]  __jump_label_update+0xef/0x350
[]  __static_key_slow_dec_cpuslocked.part.0+0x3c/0x60
[]  jump_label_update_timeout+0x2c/0x40
[]  process_one_work+0xe3b/0x1670
[]  worker_thread+0x587/0xce0
[]  kthread+0x28a/0x350
[]  ret_from_fork+0x31/0x70
[]  ret_from_fork_asm+0x1a/0x30
[]  </TASK>
[] Modules linked in: veth
[] ---[ end trace 0000000000000000 ]---
[] RIP: 0010:__jump_label_patch+0x2f6/0x350

[1]: https://netdev-3.bots.linux.dev/vmksft-tcp-ao-dbg/results/696681/5-connect-deny-ipv6/stderr

Cc: stable@...nel.org
Fixes: 67fa83f7c86a ("net/tcp: Add static_key for TCP-AO")
Signed-off-by: Dmitry Safonov <0x7f454c46@...il.com>
---
---
 net/ipv4/tcp_ao.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/net/ipv4/tcp_ao.c b/net/ipv4/tcp_ao.c
index 85531437890c..5ce914d3e3db 100644
--- a/net/ipv4/tcp_ao.c
+++ b/net/ipv4/tcp_ao.c
@@ -267,6 +267,14 @@ static void tcp_ao_key_free_rcu(struct rcu_head *head)
 	kfree_sensitive(key);
 }

+static void tcp_ao_info_free_rcu(struct rcu_head *head)
+{
+	struct tcp_ao_info *ao = container_of(head, struct tcp_ao_info, rcu);
+
+	kfree(ao);
+	static_branch_slow_dec_deferred(&tcp_ao_needed);
+}
+
 void tcp_ao_destroy_sock(struct sock *sk, bool twsk)
 {
 	struct tcp_ao_info *ao;
@@ -290,9 +298,7 @@ void tcp_ao_destroy_sock(struct sock *sk, bool twsk)
 			atomic_sub(tcp_ao_sizeof_key(key), &sk->sk_omem_alloc);
 		call_rcu(&key->rcu, tcp_ao_key_free_rcu);
 	}
-
-	kfree_rcu(ao, rcu);
-	static_branch_slow_dec_deferred(&tcp_ao_needed);
+	call_rcu(&ao->rcu, tcp_ao_info_free_rcu);
 }

 void tcp_ao_time_wait(struct tcp_timewait_sock *tcptw, struct tcp_sock *tp)

---
base-commit: c33ffdb70cc6df4105160f991288e7d2567d7ffa
change-id: 20240725-tcp-ao-static-branch-rcu-85ede7b3a1a5

Best regards,
-- 
Dmitry Safonov <0x7f454c46@...il.com>