linux-kernel - [PATCH] net: tls: wait for async completion on last message

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Message-Id: <20240904-ktls-wait-async-v1-1-a62892833110@pengutronix.de>
Date: Wed, 04 Sep 2024 14:17:41 +0200
From: Sascha Hauer <s.hauer@...gutronix.de>
To: Boris Pismenny <borisp@...dia.com>, 
 John Fastabend <john.fastabend@...il.com>, Jakub Kicinski <kuba@...nel.org>, 
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
 Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Jens Axboe <axboe@...nel.dk>, Pavel Begunkov <asml.silence@...il.com>, 
 kernel@...gutronix.de, Sascha Hauer <s.hauer@...gutronix.de>
Subject: [PATCH] net: tls: wait for async completion on last message

When asynchronous encryption is used KTLS sends out the final data at
proto->close time. This becomes problematic when the task calling
close() receives a signal. In this case it can happen that
tcp_sendmsg_locked() called at close time returns -ERESTARTSYS and the
final data is not sent.

The described situation happens when KTLS is used in conjunction with
io_uring, as io_uring uses task_work_add() to add work to the current
userspace task. A discussion of the problem along with a reproducer can
be found in [1] and [2]

Fix this by waiting for the asynchronous encryption to be completed on
the final message. With this there is no data left to be sent at close
time.

[1] https://lore.kernel.org/all/20231010141932.GD3114228@pengutronix.de/
[2] https://lore.kernel.org/all/20240315100159.3898944-1-s.hauer@pengutronix.de/

Signed-off-by: Sascha Hauer <s.hauer@...gutronix.de>
---

A previous attempt to solve this problem can be found here:

https://lore.kernel.org/all/20240410-ktls-defer-close-v1-1-b59e6626b8e4@pengutronix.de/

This patch had KASAN issues when running the tls selftests. This is
a new approach, solving the issue at send time, not at close time. This
patch can now run the tls selftests successfully.
---
 net/tls/tls_sw.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c
index 305a412785f50..bbf26cc4f6ee2 100644
--- a/net/tls/tls_sw.c
+++ b/net/tls/tls_sw.c
@@ -1201,7 +1201,7 @@ static int tls_sw_sendmsg_locked(struct sock *sk, struct msghdr *msg,

 	if (!num_async) {
 		goto send_end;
-	} else if (num_zc) {
+	} else if (num_zc || eor) {
 		int err;

 		/* Wait for pending encryptions to get completed */

---
base-commit: 431c1646e1f86b949fa3685efc50b660a364c2b6
change-id: 20240904-ktls-wait-async-0a4e9a513f6f

Best regards,
-- 
Sascha Hauer <s.hauer@...gutronix.de>