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smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=cLbZJUt0; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="cLbZJUt0" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4A7C5C16AAE; Thu, 13 Nov 2025 08:47:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1763023676; bh=RmKNA6H3doE5+IR1gbtiers6aYu4NZKwetGeD2EFal8=; h=Date:Subject:To:References:From:Cc:In-Reply-To:From; b=cLbZJUt0QOKXjFyKW08MZQs1ghQtVDddjFacX6KMyXRYGCEdlN6fjKORHc19nXrck vdgzdoU46Fc7Tvlq3PvN9c1yNAJAInaMB/7Y7j97lEMRDMov6s0aT1niltFupZ7t31 Hcav2WHsNt3oZjMdbJyh28yaylB7MghYsPr1eE7VHpccijRADnPGW+r6oHmNWtkgC1 LtI4F6EvPSOncy7sFJ26Eq6pvP6pA4Qp2oPc7wTPCUgDWNRbJhJk4nD8IaiZiqp533 1YpuY9qmwJDVPlKfWY90skIkhhD6LF19Ejf5Ugo5jw6z2QQd9Rxgy0CyFKsRFmsE6H HYo4XUy0VR7/w== Message-ID: <49c300cc-e000-420d-82ad-aa59e5f1cd76@kernel.org> Date: Thu, 13 Nov 2025 09:47:54 +0100 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 v3 mptcp-net 1/3] mptcp: fix grafting corner case Content-Language: en-GB, fr-BE To: Paolo Abeni References: <4696be966622c9d340e8bfa4728b219b7cac1d1b.1762992570.git.pabeni@redhat.com> From: Matthieu Baerts Autocrypt: addr=matttbe@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit Hi Paolo, On 13/11/2025 01:10, Paolo Abeni wrote: > If a passive MPTCP socket creates active subflows while still unaccepted, > __mptcp_subflow_connect() will try to graft such subflows to the msk, > but the msk struct socket is not yet initialized at that point: > the subflows will misbehave. What kind of errors were visible? > Address the issue always trying to graft the subflow in > mptcp_finish_join(), regardless of the subflow itself being active or > passive. To avoid races with accept(), access the msk->sk_socket under > the callback lock. Thank you for addressing this issue! > By chance, do you have a Fixes tag to add here? (if it is for -net) > Signed-off-by: Paolo Abeni > --- > net/mptcp/protocol.c | 23 +++++++++++++++++------ > 1 file changed, 17 insertions(+), 6 deletions(-) > > diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c > index 8965abb94b81..1b3c5fd01600 100644 > --- a/net/mptcp/protocol.c > +++ b/net/mptcp/protocol.c > @@ -913,12 +913,6 @@ static bool __mptcp_finish_join(struct mptcp_sock *msk, struct sock *ssk) > mptcp_subflow_joined(msk, ssk); > spin_unlock_bh(&msk->fallback_lock); > > - /* attach to msk socket only after we are sure we will deal with it > - * at close time > - */ > - if (sk->sk_socket && !ssk->sk_socket) > - mptcp_sock_graft(ssk, sk->sk_socket); > - > mptcp_subflow_ctx(ssk)->subflow_id = msk->subflow_id++; > mptcp_sockopt_sync_locked(msk, ssk); > mptcp_stop_tout_timer(sk); > @@ -3734,6 +3728,20 @@ void mptcp_sock_graft(struct sock *sk, struct socket *parent) > write_unlock_bh(&sk->sk_callback_lock); > } > > +static void mptcp_check_graft(struct sock *sk, struct sock *ssk) > +{ > + struct socket *sock; > + > + if (ssk->sk_socket) > + return; > + > + write_lock_bh(&sk->sk_callback_lock); > + sock = sk->sk_socket; > + write_lock_bh(&sk->sk_callback_lock); The build job failed because here it should be the unlock version (write_unlock_bh()). (and probably an empty line just after). If there is only that, I can fix that when applying the patches. > + if (sock) > + mptcp_sock_graft(ssk, sock); > +} > + > bool mptcp_finish_join(struct sock *ssk) > { > struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk); > @@ -3758,6 +3766,7 @@ bool mptcp_finish_join(struct sock *ssk) > } > mptcp_subflow_joined(msk, ssk); > spin_unlock_bh(&msk->fallback_lock); > + mptcp_check_graft(parent, ssk); > mptcp_propagate_sndbuf(parent, ssk); > return true; > } > @@ -3767,6 +3776,8 @@ bool mptcp_finish_join(struct sock *ssk) > goto err_prohibited; > } > > + mptcp_check_graft(parent, ssk); Is it OK to graft it even in case of errors in __mptcp_finish_join()? i.e. not in an established state or !msk->allow_subflows. Should it not be done after the block below, if there was no error? > + > /* If we can't acquire msk socket lock here, let the release callback > * handle it > */ Cheers, Matt -- Sponsored by the NGI0 Core fund.