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 ED0A13783B4; Fri, 28 Aug 2026 09:59:03 +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=1787911145; cv=none; b=sAgG5faIykFBMZ/W7wTeVYmsImSbkso4KIiY1NNfi03/7YD9qOHC84nVJyYjcZPM9X1oQOfaVVf5oayghOh/Z2nfGlE9ayNoKsF7ioXBNNah1jY5fbRot7+EEKneSFMEAppJuCG/N7EzctpCjV0vAq1Owjoq6OgwrTDJHoo3rcY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787911145; c=relaxed/simple; bh=rh7ydI7GKJqG6nY9dYE/lkWRfceAJLLwblnkmdTBs90=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=m+lwJPD4ubHFiOWMjQgXEavrJVmLwSn/dsDLzrPFrwr5AIgnf8IWt75ANSFTF4Fsb4B5P0fuDM8cLIwTp7lqTkE+2fhgLvD0ES04JGCLY0GI0idykXbDDViMG5auUxkaD62YWWrOipvOhq9c8oMtaeW1kkj3OrZStDd0biLMLLI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=LhfgIKc7; 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="LhfgIKc7" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 06E1E1F000E9; Fri, 28 Aug 2026 09:59:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787911143; bh=2+/PLbq9eAr3WZpjlc5dc0ni8rDbxUE+V7YrchB1cDk=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=LhfgIKc7j1RnY8NAmPSkj953ILT5SymGzndUyAhN2IQmM9nruMTa5dI7q/t/DVrXd 4PWk1+8AUg7TJA9LMDVHeQ/vc/XBFvgc8Wg/4F+ygYZGoUPSbGyx9xbibnd70Y7udR 935JD3KHYzGcOgZ+oGle9Q/wGxayTZC+YsoYIh6pM8gZQfi+7Nfp9qBymjxOC840T5 kePJdh6B+W08eYGhJvpF+X7S3/EyOa+pD0ZT4ne3L/FAeo60E+l+tdk52cW83Bqy4j DEMC+l+AXPbXbqdFJnYcyKs9JiPqxgPksGCyS1NhHK5pzgvBcwy/sFPVdkDj6nHT6Z lqwMMfIOK5Aqw== Message-ID: Date: Fri, 28 Aug 2026 11:58:58 +0200 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Beta Subject: Re: [PATCH net 02/14] mptcp: subflow: no need to copy thmac during ulp_clone Content-Language: fr To: Jakub Kicinski Cc: martineau@kernel.org, geliang@kernel.org, davem@davemloft.net, edumazet@google.com, pabeni@redhat.com, horms@kernel.org, netdev@vger.kernel.org, mptcp@lists.linux.dev, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20260824-net-mptcp-misc-fixes-7-3-rc1-v1-2-a92309d121ca@kernel.org> <20260827190725.3998222-1-kuba@kernel.org> From: Matthieu Baerts Autocrypt: addr=matttbe@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit Hi Jakub, On 27/08/2026 21:07, Jakub Kicinski wrote: > This is an AI-generated review of your patch. The human sending this > email has considered the AI review valid, or at least plausible. Thank you for having forwarded this, I didn't manage to look at it before. > --- > mptcp: subflow: no need to copy thmac during ulp_clone > > This drops the copy of subflow_req->thmac into the new subflow context in > subflow_ulp_clone(), since the truncated HMAC is no longer needed once the > passive-side request is over. The commit message notes that thmac is left > uninitialised on the SYN cookie path, so removing the copy also avoids a > KMSAN uninitialised-read report. > > (no Link: tags in the commit header) > >> diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c >> index af81ad5e699d1..01db7edce18a6 100644 >> --- a/net/mptcp/subflow.c >> +++ b/net/mptcp/subflow.c >> @@ -2084,7 +2084,6 @@ static void subflow_ulp_clone(const struct request_sock *req, >> new_ctx->request_bkup = subflow_req->request_bkup; > ^^^^ > > [Severity: Medium] > This isn't a bug introduced by this patch, but while looking at the > neighbouring store: does request_bkup have exactly the same > uninitialised-on-SYN-cookies problem that motivated removing the thmac > copy here? > > subflow_init_req() only clears a subset of the fields: > > net/mptcp/subflow.c:subflow_init_req() { > subflow_req->mp_capable = 0; > subflow_req->mp_join = 0; > subflow_req->csum_reqd = mptcp_is_checksum_enabled(sock_net(sk_listener)); > subflow_req->allow_join_id0 = mptcp_allow_join_id0(sock_net(sk_listener)); > subflow_req->msk = NULL; > mptcp_token_init_request(req); > } > > and the only assignment of request_bkup for a request sock happens on the > SYN, in subflow_token_join_request(): > > subflow_req->local_id = local_id; > subflow_req->request_bkup = mptcp_pm_is_backup(msk, (struct sock_common *)req); > > On the cookie ACK path that function is not called, and the state restore > does not cover request_bkup either: > > net/mptcp/syncookies.c:mptcp_token_join_cookie_init_state() { > subflow_req->remote_nonce = e->remote_nonce; > subflow_req->local_nonce = e->local_nonce; > subflow_req->backup = e->backup; > subflow_req->remote_id = e->join_id; > subflow_req->local_id = e->local_id; > subflow_req->token = e->token; > subflow_req->msk = msk; > } > > struct join_entry has no request_bkup member at this commit, so the bit > carries whatever was in the freshly allocated request sock. > > Unlike thmac, the copied value is consumed afterwards, for instance in > mptcp_subflow_get_send() and mptcp_subflow_get_retrans(): > > net/mptcp/protocol.c:mptcp_subflow_get_send() { > bool backup = subflow->backup || subflow->request_bkup; > > It is also put on the wire by mptcp_established_options_mp_prio() and > exported to userspace by the mptcp diag code. > > So when a remote MP_JOIN is accepted while tcp_syncookies is active, can a > joined subflow end up randomly flagged as backup and reported that way in > diag, along with the same class of KMSAN uninit-value branch report that > this patch removes for thmac? > > For the record, the next patch in this series, "mptcp: syncookies: remember > the request backup flag", adds request_bkup:1 to struct join_entry and > stores/restores it, and the store happens after subflow_token_join_request() > has set the field (subflow_token_join_request() runs before > subflow_init_req_cookie_join_save() in subflow_check_req()), so the field is > properly initialised at the end of the series. All of this to say that it is fixed in the next patch... > Would it be worth mentioning > that dependency here, given this patch carries a Cc: stable tag? Do we really need to mention that?? This report says "there is a pre-existing bug in the code around", then there is no direct dependence. Or should we add for each patch: other fixes follow this one? Note that there is an issue on Sashiko's side to improve that: https://github.com/sashiko-dev/sashiko/issues/392 Cheers, Matt -- Sponsored by the NGI0 Core fund.