From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 1DB06318EEE; Mon, 4 May 2026 09:37:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777887441; cv=none; b=P3pEqRc9LtL7QQ+ybHV2LV3AJENqGieuITbgWCyxBxPiAvBXNgNnW7KFWE/EYsF5xAPeki6LNckecfqVs+9ZZrgdklxeY+hnYqP0l2wLK+mPVyJElqdV8sf7LkYs3RYYiJe+t7nabHE2SrCRDSFRmH6RRap+07rDd85RIsqN8tc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777887441; c=relaxed/simple; bh=4eF9TbJhAf3/z7VfA2M6NFnSc+hISwqkU7Bk9HQMgyE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ZOb+bP4lQNPVeQPMU4/r7JXiYK3ifLdFhLcl4te+lE+U/M0cNm53z6ok5v8ntJvaSAmP3fV72srJba78wqJsCoOvtpQTL8Q2n3D/y02bBhdQgCRddW71LuQc38is6VCpH6lyKd7Ka0a4+0l+UABynCXwnOaZUu56vY1EuqoDAmM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=G8ziYwAx; 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="G8ziYwAx" Received: by smtp.kernel.org (Postfix) with ESMTPSA id F1E72C2BCB9; Mon, 4 May 2026 09:37:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1777887440; bh=4eF9TbJhAf3/z7VfA2M6NFnSc+hISwqkU7Bk9HQMgyE=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=G8ziYwAxUZqs9GG2X/xaz3ITYOMOV26Q2YYjekFO7uniMgm23RL0itdX8E8CVOmEx 8ueT3Oj/uoiadUlLjZLr4xcHz/j8Gw/0iX+Ie0OSobKmf7QNBAnwJE0pV5TSkrQDG4 vwFKB8sV6Gwel/bdyKEEDlwz4k004559VtqFr4tVhaCHDXWnww3hKhelZdnvlb6kFt fuqUMGAOd0iMwh9ppGin2UtVD9mx8/8Sdngw3foU9gjlliA29DvgWObNWvwJQFRWpU DVfdpZ3SJPmUdjQTrPVv2bQrfqx8OMwIOcaEZ5qP4ZKCjo10UP2fzlv3FM4ZyP0wyU ZemtbVJ6z5ApA== Message-ID: <03e9b128-109c-41fb-9147-0cf9b6127d73@kernel.org> Date: Mon, 4 May 2026 11:37:14 +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] mptcp: zero opts->ext_copy in mptcp_established_options_dss() To: Deepanshu Kartikey , martineau@kernel.org, geliang@kernel.org, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org Cc: cpaasch@apple.com, netdev@vger.kernel.org, mptcp@lists.linux.dev, linux-kernel@vger.kernel.org, syzbot+ff020673c5e3d94d9478@syzkaller.appspotmail.com References: <20260504003156.11125-1-kartikey406@gmail.com> From: Matthieu Baerts Content-Language: fr Autocrypt: addr=matttbe@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit Hi Deepanshu, On 04/05/2026 02:31, Deepanshu Kartikey wrote: > syzbot reported a KMSAN uninit-value in mptcp_write_data_fin() reached > via tcp_send_ack() from the subflow shutdown path: > > BUG: KMSAN: uninit-value in mptcp_write_data_fin net/mptcp/options.c:542 > mptcp_established_options_dss net/mptcp/options.c:590 > mptcp_established_options net/mptcp/options.c:874 > tcp_established_options net/ipv4/tcp_output.c:1192 > __tcp_transmit_skb net/ipv4/tcp_output.c:1575 > __tcp_send_ack net/ipv4/tcp_output.c:4499 > tcp_send_ack net/ipv4/tcp_output.c:4505 > mptcp_subflow_shutdown net/mptcp/protocol.c:3137 > mptcp_check_send_data_fin net/mptcp/protocol.c:3218 > __mptcp_wr_shutdown net/mptcp/protocol.c:3234 > __mptcp_close net/mptcp/protocol.c:3313 > > Local variable opts created at: > __tcp_transmit_skb net/ipv4/tcp_output.c:1536 > > __tcp_transmit_skb() partially clears its on-stack tcp_out_options via > "memset(&opts.cleared, ...)" which does not cover opts.mptcp, so MPTCP > is responsible for initializing opts->ext_copy before use. > > mptcp_established_options_dss() only writes opts->ext_copy when an > MPTCP extension is attached to the skb ("opts->ext_copy = *mpext"). > When tcp_send_ack() builds a fresh pure-ACK skb during subflow > shutdown, the skb has no extension and that assignment is skipped, but > the function still calls mptcp_write_data_fin(&opts->ext_copy) because > snd_data_fin_enable is set. mptcp_write_data_fin() then reads > ext->use_map to choose between writing a synthetic DATA_FIN mapping or > extending an existing one, and that read hits uninitialized stack > memory. > > Zero opts->ext_copy at the top of mptcp_established_options_dss() so > mptcp_write_data_fin() takes its synthetic-mapping branch on clean > memory. Thank you for sharing this patch! Kuniyuki already shared the same patch on the MPTCP ML a few days ago: https://lore.kernel.org/mptcp/20260501061939.1808489-1-kuniyu@google.com/T/#u A v2 has been shared a few hours ago: https://lore.kernel.org/mptcp/20260504044051.3725846-1-kuniyu@google.com/T/#u (and apparently, a v3 will be needed) Cheers, Matt -- pw-bot: Rejected Sponsored by the NGI0 Core fund.