From: Jakub Sitnicki <jakub@cloudflare.com>
To: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: netdev@vger.kernel.org, "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: Mon, 21 Nov 2022 10:00:09 +0100 [thread overview]
Message-ID: <871qpw8ywt.fsf@cloudflare.com> (raw)
In-Reply-To: <f8e54710-6889-5c27-2b3c-333537495ecd@I-love.SAKURA.ne.jp>
On Sat, Nov 19, 2022 at 10:52 PM +09, 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.
You're right. v2 posted:
https://lore.kernel.org/netdev/20221121085426.21315-1-jakub@cloudflare.com/
prev parent reply other threads:[~2022-11-21 9:01 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
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 [this message]
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