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Message-Id: <20230227-upstream-net-20230227-mptcp-fixes-v1-1-070e30ae4a8e@tessares.net> Date: Mon, 27 Feb 2023 18:29:24 +0100 From: Matthieu Baerts <matthieu.baerts@...sares.net> To: mptcp@...ts.linux.dev, "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Menglong Dong <imagedong@...cent.com>, Mengen Sun <mengensun@...cent.com>, Shuah Khan <shuah@...nel.org>, Florian Westphal <fw@...len.de>, Jiang Biao <benbjiang@...cent.com> Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org, Matthieu Baerts <matthieu.baerts@...sares.net>, stable@...r.kernel.org, Christoph Paasch <cpaasch@...le.com> Subject: [PATCH net 1/7] mptcp: fix possible deadlock in subflow_error_report From: Paolo Abeni <pabeni@...hat.com> Christoph reported a possible deadlock while the TCP stack destroys an unaccepted subflow due to an incoming reset: the MPTCP socket error path tries to acquire the msk-level socket lock while TCP still owns the listener socket accept queue spinlock, and the reverse dependency already exists in the TCP stack. Note that the above is actually a lockdep false positive, as the chain involves two separate sockets. A different per-socket lockdep key will address the issue, but such a change will be quite invasive. Instead, we can simply stop earlier the socket error handling for orphaned or unaccepted subflows, breaking the critical lockdep chain. Error handling in such a scenario is a no-op. Fixes: 15cc10453398 ("mptcp: deliver ssk errors to msk") Cc: stable@...r.kernel.org Reported-and-tested-by: Christoph Paasch <cpaasch@...le.com> Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/355 Signed-off-by: Paolo Abeni <pabeni@...hat.com> Reviewed-by: Matthieu Baerts <matthieu.baerts@...sares.net> Signed-off-by: Matthieu Baerts <matthieu.baerts@...sares.net> --- net/mptcp/subflow.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c index 4ae1a7304cf0..5070dc33675d 100644 --- a/net/mptcp/subflow.c +++ b/net/mptcp/subflow.c @@ -1432,6 +1432,13 @@ static void subflow_error_report(struct sock *ssk) { struct sock *sk = mptcp_subflow_ctx(ssk)->conn; + /* bail early if this is a no-op, so that we avoid introducing a + * problematic lockdep dependency between TCP accept queue lock + * and msk socket spinlock + */ + if (!sk->sk_socket) + return; + mptcp_data_lock(sk); if (!sock_owned_by_user(sk)) __mptcp_error_report(sk); -- 2.38.1
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