From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
To: Jakub Sitnicki <jakub@cloudflare.com>, netdev@vger.kernel.org
Cc: "David S. Miller" <davem@davemloft.net>,
Eric Dumazet <edumazet@google.com>,
Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
Tom Parkin <tparkin@katalix.com>,
syzbot+703d9e154b3b58277261@syzkaller.appspotmail.com,
syzbot+50680ced9e98a61f7698@syzkaller.appspotmail.com,
syzbot+de987172bb74a381879b@syzkaller.appspotmail.com
Subject: Re: [PATCH net] l2tp: Don't sleep and disable BH under writer-side sk_callback_lock
Date: Sat, 19 Nov 2022 23:27:54 +0900 [thread overview]
Message-ID: <a850c224-f728-983c-45a0-96ebbaa943d7@I-love.SAKURA.ne.jp> (raw)
In-Reply-To: <f8e54710-6889-5c27-2b3c-333537495ecd@I-love.SAKURA.ne.jp>
On 2022/11/19 22:52, Tetsuo Handa wrote:
> On 2022/11/19 22:03, Jakub Sitnicki wrote:
>> When holding a reader-writer spin lock we cannot sleep. Calling
>> setup_udp_tunnel_sock() with write lock held violates this rule, because we
>> end up calling percpu_down_read(), which might sleep, as syzbot reports
>> [1]:
>>
>> __might_resched.cold+0x222/0x26b kernel/sched/core.c:9890
>> percpu_down_read include/linux/percpu-rwsem.h:49 [inline]
>> cpus_read_lock+0x1b/0x140 kernel/cpu.c:310
>> static_key_slow_inc+0x12/0x20 kernel/jump_label.c:158
>> udp_tunnel_encap_enable include/net/udp_tunnel.h:187 [inline]
>> setup_udp_tunnel_sock+0x43d/0x550 net/ipv4/udp_tunnel_core.c:81
>> l2tp_tunnel_register+0xc51/0x1210 net/l2tp/l2tp_core.c:1509
>> pppol2tp_connect+0xcdc/0x1a10 net/l2tp/l2tp_ppp.c:723
>>
>> Trim the writer-side critical section for sk_callback_lock down to the
>> minimum, so that it covers only operations on sk_user_data.
>
> This patch does not look correct.
>
> Since l2tp_validate_socket() checks that sk->sk_user_data == NULL with
> sk->sk_callback_lock held, you need to call rcu_assign_sk_user_data(sk, tunnel)
> before releasing sk->sk_callback_lock.
>
Is it safe to temporarily set a dummy pointer like below?
If it is not safe, what makes assignments done by setup_udp_tunnel_sock() safe?
diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index 754fdda8a5f5..198d38d8fceb 100644
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -1474,11 +1474,12 @@ int l2tp_tunnel_register(struct l2tp_tunnel *tunnel, struct net *net,
}
sk = sock->sk;
- write_lock(&sk->sk_callback_lock);
-
+ write_lock_bh(&sk->sk_callback_lock);
ret = l2tp_validate_socket(sk, net, tunnel->encap);
if (ret < 0)
goto err_sock;
+ rcu_assign_sk_user_data(sk, (void *) 1);
+ write_unlock_bh(&sk->sk_callback_lock);
tunnel->l2tp_net = net;
pn = l2tp_pernet(net);
@@ -1492,6 +1493,8 @@ int l2tp_tunnel_register(struct l2tp_tunnel *tunnel, struct net *net,
spin_unlock_bh(&pn->l2tp_tunnel_list_lock);
sock_put(sk);
ret = -EEXIST;
+ write_lock_bh(&sk->sk_callback_lock);
+ rcu_assign_sk_user_data(sk, NULL);
goto err_sock;
}
}
@@ -1522,16 +1525,15 @@ int l2tp_tunnel_register(struct l2tp_tunnel *tunnel, struct net *net,
if (tunnel->fd >= 0)
sockfd_put(sock);
- write_unlock(&sk->sk_callback_lock);
return 0;
err_sock:
+ write_unlock_bh(&sk->sk_callback_lock);
+
if (tunnel->fd < 0)
sock_release(sock);
else
sockfd_put(sock);
-
- write_unlock(&sk->sk_callback_lock);
err:
return ret;
}
next prev parent reply other threads:[~2022-11-19 14:28 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-19 13:03 [PATCH net] l2tp: Don't sleep and disable BH under writer-side sk_callback_lock Jakub Sitnicki
2022-11-19 13:52 ` Tetsuo Handa
2022-11-19 14:27 ` Tetsuo Handa [this message]
2022-11-21 9:00 ` Jakub Sitnicki
2022-11-21 10:03 ` Tetsuo Handa
2022-11-21 21:55 ` Jakub Sitnicki
2022-11-22 9:48 ` Tetsuo Handa
2022-11-22 10:46 ` Jakub Sitnicki
2022-11-22 11:14 ` Tetsuo Handa
2022-11-22 14:10 ` Guillaume Nault
2022-11-22 14:28 ` Tetsuo Handa
2022-11-23 15:24 ` Guillaume Nault
2022-11-24 10:07 ` Tom Parkin
2022-11-24 10:27 ` Guillaume Nault
2022-11-21 9:00 ` Jakub Sitnicki
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=a850c224-f728-983c-45a0-96ebbaa943d7@I-love.SAKURA.ne.jp \
--to=penguin-kernel@i-love.sakura.ne.jp \
--cc=davem@davemloft.net \
--cc=edumazet@google.com \
--cc=jakub@cloudflare.com \
--cc=kuba@kernel.org \
--cc=netdev@vger.kernel.org \
--cc=pabeni@redhat.com \
--cc=syzbot+50680ced9e98a61f7698@syzkaller.appspotmail.com \
--cc=syzbot+703d9e154b3b58277261@syzkaller.appspotmail.com \
--cc=syzbot+de987172bb74a381879b@syzkaller.appspotmail.com \
--cc=tparkin@katalix.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).