From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 44EB74746BE for ; Wed, 12 Aug 2026 15:32:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786548754; cv=none; b=glykHah7Q4p+MkV20FdsuOQS7nUmMQYjSFQC5mzzOtfJ7Flog7Qn756IXBnmCbKGo1WeC4rrmasKZc39folyC09tbI6Zx6M66ufDcslE1AY8/UcBVyDqCRvdKmLwbugp/zOyFpputdSIXLfoelyZLiQO7r4O5kObR1V4+B+D77E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786548754; c=relaxed/simple; bh=jhr1nRmKKSUafi1Fq+WoM8rnnyPERpHT3v9mB7icMCU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=AoZR9lvD7UTqILA/FaN4vty3PVrd0O3alEcgPp0FVc2db6++Qt3GbZJZIG7TY8BTWaJW1HvcHSULUfw0FjJIVkOhZPU4OmH1SsD1KospNa7XvZxCOyDLuM83OwgF2p+GGUoVsWbkg/0fktIIYCIXKThtStIDvnYz5gQSaBW4vps= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=dUtxxpxz; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="dUtxxpxz" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CF2491F000E9; Wed, 12 Aug 2026 15:32:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786548743; bh=Q0IGxxB0TfVEauRh+67tFMZVgrJ/a/eNcPicZOY1ORE=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=dUtxxpxzR39MswWSWirRobzAWG2OWnuKmsBrTmTFDU8h9aef4GN89ARzl30VmF2e2 RgUamHRPLv39Z4xRSI8fP2JT9G3PyXpM0soHgfs3rvKAH4ykBiYarFKfw6fGwb+B4M q+DwB1wmeQfD1x4nmnbnIUClkzTB6NU5HS42DIiyXh5ySudQ/Cvx90zPWkD108osTY y327l081Ba53A7ITAc9xmmT1Z8PeXkffm7D4zl/lXtTmqUooEoKudM/dbW9Iz5to5e TdRZrLvrIBtBz010gs6MK4pUXcYSnQEK8vt4S5aHi6iL0Mne9P30nvRa5xVNmLMtd5 PXAIsBOqPko+A== Message-ID: <41078a8c-00c7-4cb1-8e57-237b4ea6c2f0@kernel.org> Date: Wed, 12 Aug 2026 17:32:21 +0200 Precedence: bulk X-Mailing-List: mptcp@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Beta Subject: Re: [PATCH export v3 2/4] mptcp: reject joins after fallback in mptcp_is_fully_established Content-Language: fr To: Paolo Abeni , Chenguang Zhao , mptcp@lists.linux.dev Cc: Chenguang Zhao References: <20260812054653.43799-1-chenguang.zhao@linux.dev> <20260812054653.43799-3-chenguang.zhao@linux.dev> <1d7c56b9-00c1-4550-a403-c3d704259267@redhat.com> From: Matthieu Baerts Autocrypt: addr=matttbe@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit Hi Paolo, Chenguang, On 12/08/2026 11:45, Paolo Abeni wrote: > On 8/12/26 7:46 AM, Chenguang Zhao wrote: >> From: Chenguang Zhao >> >> After fallback, treat the connection as not fully established so later >> MP_JOIN attempts are rejected. @Chenguang: please first reply to the questions and comments from the previous versions, then only send a new version when the discussions are over. >> Signed-off-by: Chenguang Zhao >> --- >> net/mptcp/protocol.h | 5 ++++- >> 1 file changed, 4 insertions(+), 1 deletion(-) >> >> diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h >> index 7e168e450fb0..bf2483a7ed92 100644 >> --- a/net/mptcp/protocol.h >> +++ b/net/mptcp/protocol.h >> @@ -957,8 +957,11 @@ static inline void mptcp_start_tout_timer(struct sock *sk) >> >> static inline bool mptcp_is_fully_established(struct sock *sk) >> { >> + struct mptcp_sock *msk = mptcp_sk(sk); >> + >> return inet_sk_state_load(sk) == TCP_ESTABLISHED && >> - READ_ONCE(mptcp_sk(sk)->fully_established); >> + READ_ONCE(msk->fully_established) && >> + !test_bit(MPTCP_FALLBACK_DONE, &msk->flags); > > Does the above improve actually anything? The test is inherently racy, > as lack the fallback_lock, and AFAICS all critical paths have already > explicit checks under such lock, see i.e. mptcp_finish_join(). Indeed, the fallback lock is missing. Note: Chenguang is looking at a bug where, when an MP_FAIL is received before being in fully_established, the kernel accept going to fully established, and creating new subflows, then reject them once done. Same when receiving a 4th packet without MPTCP options. I think the MP_FAIL should do a fallback if possible, but it is probably also required to check the fallback status or something similar when receiving an MPJ. > I would prefer avoiding additional conditionals, if not well reasoned. Agreed, the commit messages in this series are not explaining (enough) the reason and the context. BTW, Chenguang, please use 'mptcp-net' for fixes (and mptcp-next for features). Also fixes should have a Fixes tag. Cheers, Matt -- Sponsored by the NGI0 Core fund.