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smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=P/8mOZ5N; 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="P/8mOZ5N" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 668D0C4CEEF; Thu, 31 Jul 2025 09:59:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1753956000; bh=QeKUVb4lpwhFP4ae4SyPkUvf9Mi0i/yZg/Q0hULVNwU=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=P/8mOZ5Nc1eHzOjxtb5DigqrW7/E6IRbys1c9PjeRLyzFIwNdgPV6VYcukowXNvog 0hbp0PKTJGlqi/WvQUHNElFXdvBH/wa6PC/uh/ItTAszy/0CqsLTuWkQE/tVfeK2rm Tl57fej+K45bS3EcChjLBnSNfkVXU8eMwNZyOg85kw2zEKJn6oRIbNp5QF9WfA1KqQ +wvxVmNaQWm7JYxl36sWm2bijjw396uvS4g8tVNk0khk89Do/l7/96YV2dY1MLg2vL pOsIS1/BRifSaHyvT+4vYQKrJs0Z5aScRvw3ME2sXLcLgf5v7LjaclzggXlYdAjA3F FhIGSpwfmDXdw== Message-ID: <9f6237d3-a8eb-4dce-bea1-baefbd6ef59c@kernel.org> Date: Thu, 31 Jul 2025 11:59:57 +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 mptcp-next v2 2/2] mptcp: setsockopt support for TCP_MD5SIG Content-Language: en-GB, fr-BE To: Geliang Tang , mptcp@lists.linux.dev Cc: Geliang Tang References: <291bace9364966f432580ba13121bd59677f5d3e.1753946671.git.tanggeliang@kylinos.cn> From: Matthieu Baerts Autocrypt: addr=matttbe@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit Hi Geliang, Thank you for the new version. On 31/07/2025 09:27, Geliang Tang wrote: > From: Geliang Tang > > This adds setsockopt support for TCP_MD5SIG and TCP_MD5SIG_EXT options. > The implementation: > - Allows setting these options (getsockopt remains unsupported) > - Applies them only to the first subflow > - Forces fallback to TCP (since MD5 isn't compatible with MPTCP) > > Setting these options triggers fallback to TCP to maintain MD5 > compatibility. > > Note that TCP_MD5SIG and TCP_MD5SIG_EXT are unsupported for TCP too. > > Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/575 > Signed-off-by: Geliang Tang > --- > net/mptcp/sockopt.c | 12 ++++++++++-- > 1 file changed, 10 insertions(+), 2 deletions(-) > > diff --git a/net/mptcp/sockopt.c b/net/mptcp/sockopt.c > index b264185b810d..3ffdeca694be 100644 > --- a/net/mptcp/sockopt.c > +++ b/net/mptcp/sockopt.c > @@ -13,6 +13,7 @@ > #include > #include > #include "protocol.h" > +#include "mib.h" > > #define MIN_INFO_OPTLEN_SIZE 16 > #define MIN_FULL_INFO_OPTLEN_SIZE 40 > @@ -567,11 +568,12 @@ static bool mptcp_supported_sockopt(int level, int optname) > case TCP_FASTOPEN_CONNECT: > case TCP_FASTOPEN_KEY: > case TCP_FASTOPEN_NO_COOKIE: > + /* MD5 will force a fallback to TCP: OK to set while not connected */ > + case TCP_MD5SIG: > + case TCP_MD5SIG_EXT: > return true; > } > > - /* TCP_MD5SIG, TCP_MD5SIG_EXT are not supported, MD5 is not compatible with MPTCP */ > - > /* TCP_REPAIR, TCP_REPAIR_QUEUE, TCP_QUEUE_SEQ, TCP_REPAIR_OPTIONS, > * TCP_REPAIR_WINDOW are not supported, better avoid this mess > */ > @@ -830,6 +832,12 @@ static int mptcp_setsockopt_sol_tcp(struct mptcp_sock *msk, int optname, > /* See tcp.c: TCP_DEFER_ACCEPT does not fail */ > mptcp_setsockopt_first_sf_only(msk, SOL_TCP, optname, optval, optlen); > return 0; > +#ifdef CONFIG_TCP_MD5SIG > + case TCP_MD5SIG: > + case TCP_MD5SIG_EXT: > + __mptcp_try_fallback(msk, MPTCP_MIB_MD5SIGFALLBACK); I don't think that's a good idea to do just that: here, you will do a fallback even if the options are not correct. Please this helper can return false if a fallback is not possible, and a reset will be needed. I think it would be easier to simply limit the use of this option for listened and closed state: a fallback will be done in mptcp_connect() and subflow_check_req(). If I'm not mistaken, mptcp_setsockopt_first_sf_only() will limit to the first subflow, before the establishment of the connection (__mptcp_nmpc_sk() is explicitly checking the state), no? Then all you require is to add the two 'case', no? If yes, please add a Fixes tag: Fixes: d9e4c1291810 ("mptcp: only admit explicitly supported sockopt") And add something like this in the commit message: Supporting TCP_MD5 socket option is required when MPTCP is used by default when creating a socket, to keep the same behaviour as with TCP. TCP_MD5 is not compatible with MPTCP, and it will cause a fallback to TCP at the connection request, if MPTCP was requested. This then fixes a "regression" compared to TCP. One last thing, please also send the new packetdrill test on GitHub when sending a next version. Cheers, Matt -- Sponsored by the NGI0 Core fund.