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 EF14736A02F; Tue, 18 Aug 2026 15:57:48 +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=1787068670; cv=none; b=i8rbvK0AcmnBsjc8rYkqB3GTvGkx2PhmTLBUYxtDN3Rv+F4SZxQZ6KMaxduxbbhlKSkF0T8SEU0OOccJW5rDk83zbKEXtn8DMzqM0XfLNjT9WpmOAJO0NJc1Usn2vBRC4lVmZfDgUoXv45khgh1tjgbWk1v//CqB19qUQeF7qT4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787068670; c=relaxed/simple; bh=wyCAOLzM8d4C2doylHsj51aWQa1LeQmbwpKGp3KeGMg=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=OZhLm9xxAq+4faJELCHcUMcSSIwF+4fdpVUiGxpm9+efWRSwz5XU2R+XPUR0VpjjAKqnLTKdV6lu1qwmTFpliTZr4FiJQ0mlkg0jS6+Vfv+CIiaM5Qj1NoWWZAINX7Qfgtm19SksszmX3dUa+k1Ieon1oeG/MgHtc5Gfv2f+5Ng= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=XeGpRteH; 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="XeGpRteH" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B37BB1F000E9; Tue, 18 Aug 2026 15:57:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787068668; bh=Yw2PJnKUma43a2n/lx8z8mSyCWYBg71MGUhxKOEG8Ac=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=XeGpRteHqTAOHNK+TGL+T6yhQa1UCaX1VuRaB/tBV2jTVvdTpI4W/B3XgLuh4v7hM 5sfHGJFGaP7xMn9E/MX2iixOBPTkbYLGWgsBoyipIUpkxlztjEKmyAyz7GMKTcOlIs F5s/Z3/zWrAPm7dbGZ/jqV+wBnmFxmCkBB23RL7q8tKn80gQlVia1HGTbE1nrsx07e zEl9wfgJm+7OfjkWcTKUq3pJQDeIQv2kQdIbDwxbinNgw734wv9AR54hbVWdBuddA0 i6qAoBfU85piFZHOJ4hO3mG4Nlt2nnHD9hyowWwCiRMFRZXhLbivweIe1/galrfSS2 gAZ8w16PhbmKw== Message-ID: Date: Tue, 18 Aug 2026 17:57:44 +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 3/5] mptcp: use READ_ONCE() over sysctls Content-Language: fr To: gang.yan@linux.dev, sashiko-reviews@lists.linux.dev Cc: mptcp@lists.linux.dev References: <20260818094825.48446-1-gang.yan@linux.dev> <20260818094825.48446-4-gang.yan@linux.dev> <20260818100151.DD70A1F00A3E@smtp.kernel.org> From: Matthieu Baerts Autocrypt: addr=matttbe@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit Hi Gang, On 18/08/2026 15:02, gang.yan@linux.dev wrote: > August 18, 2026 at 6:01 PM, sashiko-bot@kernel.org mailto:sashiko-bot@kernel.org wrote: > > >> >> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider: >> >> Pre-existing issues: >> - [High] Concurrent sysctl writes or sysctl updates racing with socket creation can leave the socket's `pm_type` and `ops` mismatched, breaking MPTCP path management. >> -- >> >> --- Patch [3]: [PATCH mptcp-next v2 3/5] mptcp: use READ_ONCE() over sysctls --- >> commit 77c9e4aa4cdd5f6c57cc4cab253d46fd0cf2dfb2 >> Author: Matthieu Baerts (NGI0) >> >> mptcp: use READ_ONCE() over sysctls >> >> This commit adds READ_ONCE() and WRITE_ONCE() macros around sysctl >> variables in the MPTCP networking code to avoid KCSAN issues. It also >> ensures the pm_type is written with WRITE_ONCE() in proc_path_manager(). >> >> Closes: https://lore.kernel.org/CANn89iL=os-60kDKqMDdyiXuPF5CG=eejS0vmthwpDGXz_Bp8A@mail.gmail.com >> >>> >>> diff --git a/net/mptcp/ctrl.c b/net/mptcp/ctrl.c >>> index c0481b09c1a17..733706f06f1b1 100644 >>> --- a/net/mptcp/ctrl.c >>> +++ b/net/mptcp/ctrl.c >>> >> [ ... ] >> >>> >>> @@ -251,7 +251,7 @@ static int proc_path_manager(const struct ctl_table *ctl, int write, >>> pm_type = MPTCP_PM_TYPE_KERNEL; >>> else if (strncmp(pm_name, "userspace", MPTCP_PM_NAME_MAX) == 0) >>> pm_type = MPTCP_PM_TYPE_USERSPACE; >>> - pernet->pm_type = pm_type; >>> + WRITE_ONCE(pernet->pm_type, pm_type); >>> >> [Severity: High] >> This is a pre-existing issue, but can this sequential update race with socket >> creation and leave the socket's pm_type and ops mismatched? >> >> If an administrator writes to the sysctl while a new socket is being created, >> could mptcp_pm_data_reset() in net/mptcp/pm.c interleave like this: >> >> CPU1 (sysctl write) >> proc_path_manager() >> mptcp_set_path_manager(pernet, pm_name); // Updates pernet->path_manager >> >> CPU2 (socket creation) >> mptcp_pm_data_reset() >> pm_type = mptcp_get_pm_type(net); // Reads old pm_type >> ... >> mptcp_get_path_manager(net, pm_name); // Reads new path_manager >> >> CPU1 (sysctl write resumes) >> proc_path_manager() >> WRITE_ONCE(pernet->pm_type, pm_type); // Updates pernet->pm_type >> >> Would this leave the new socket corrupted with a contradictory path manager >> state, breaking MPTCP path management logic? > > Hi, > > I think that may happen. Maybe need anothor patch to fix this. > > When I have time, I'll look this. Indeed, that's for another patch, probably a fix for -net. But it feels like you would need a lock to handle that properly. If it starts to be too complex, we could also say that the net.mptcp.pm_type sysctl knob is deprecated, and that's a known issue. In this case, it might be good to add a comment above this WRITE_ONCE(). Then, this could be done in a dedicated patch I think to explain why. This "mptcp: use READ_ONCE() over sysctls" would then be only about ... READ_ONCE() :) Cheers, Matt -- Sponsored by the NGI0 Core fund.