From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta1.migadu.com (out-249.mta1.migadu.com [95.215.58.249]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 31D74237180 for ; Mon, 31 Aug 2026 09:32:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.249 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788168751; cv=none; b=MQvAcDmIwtBIRNX7T/K/yI+gi9zp7vcWY/uhJLZadvdTnaJLDd7XKCie60QKb5opVH+hM5yJBApJPQiT4Isz7C/9V+SjQpZ8eLMg5w3cZJtw3Vu8ow+yxKbROp1VKFVJeYLIxoaky93oqlQgTQ6oD7Baltq9BrT1OKLGV/k8Cug= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788168751; c=relaxed/simple; bh=LPIkZ2J4gV/tmtrZ+5bcpWy0oI+XLjiiSYMdOOTkF6Q=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=k8DZMZfhpt6xxIk49DkoFZ2Ry3gzBWkR5IgvwUXsCPdL628BEwFVwxO7BFmQ/HPpjYCVKqOke//JayvX+R+omWaIfYralmnalx6GbLihmCaVvNJDaNNAZAaaIWlswWy0Vcobx5bAIxdFyd8oGkG7yN7UajWzXStsvy+A/POqjJc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=JDmeUbb6; arc=none smtp.client-ip=95.215.58.249 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="JDmeUbb6" X-Envelope-To: mptcp@lists.linux.dev DKIM-Signature: a=rsa-sha256; bh=LPIkZ2J4gV/tmtrZ+5bcpWy0oI+XLjiiSYMdOOTkF6Q=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1788168748; v=1; x=1788773548; b=JDmeUbb69LLKdkaGRPQmKX4EGTY3n5FGsKFR8KqggphnmtcdOFMVddwnH+A0l56yTAid9i6O tdYGkR5AH1K3eVRbSgquPkbcuwdwW5sJYWRscetcDILfasZZyD7TCvl53lxVfUEhQl/UWqnD/Gq DDFzMfGuuUL8/J1LfMS69KQ8= X-Envelope-To: mptcp@lists.linux.dev Received: by smtp.migadu.com with ESMTPS id 93cc3431dbaf0d27; Mon, 31 Aug 2026 09:32:27 +0000 X-Mizu-Trace-ID: 93cc3431dbaf0d27 X-Migadu-Flow: FLOW_OUT From: Tao Cui To: mptcp@lists.linux.dev Cc: matttbe@kernel.org, geliang@kernel.org, cuitao@kylinos.cn, cui.tao@linux.dev Subject: [PATCH mptcp-next 1/2] mptcp: pm: bound extra_subflows admission on userspace PM Date: Mon, 31 Aug 2026 17:32:05 +0800 Message-ID: <20260831093206.689827-2-cui.tao@linux.dev> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260831093206.689827-1-cui.tao@linux.dev> References: <20260831093206.689827-1-cui.tao@linux.dev> Precedence: bulk X-Mailing-List: mptcp@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Tao Cui mptcp_pm_allow_new_subflow() increments the u8 extra_subflows counter for every accepted MP_JOIN on sockets using the userspace PM, without any limit. A peer establishing more than 255 live subflows wraps the counter back to 0, which then makes the underflow guards warn on the next subflow close, and permanently corrupts mptcpi_subflows_total reported to userspace. Refuse new MP_JOINs once the counter has reached U8_MAX, so that it cannot wrap anymore. Fixes: e99c1ca89071 ("mptcp: pm: add WARN_ON_ONCE guards on extra_subflows underflow") Link: https://github.com/multipath-tcp/mptcp_net-next/issues/629 Signed-off-by: Tao Cui --- net/mptcp/pm.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/net/mptcp/pm.c b/net/mptcp/pm.c index 8b68868255c5..3990f6775723 100644 --- a/net/mptcp/pm.c +++ b/net/mptcp/pm.c @@ -562,10 +562,17 @@ bool mptcp_pm_allow_new_subflow(struct mptcp_sock *msk) if (mptcp_pm_is_userspace(msk)) { if (mptcp_userspace_pm_active(msk)) { + bool allow; + + /* extra_subflows is a u8: don't let a peer wrap it + * with more than U8_MAX accepted MP_JOINs + */ spin_lock_bh(&pm->lock); - pm->extra_subflows++; + allow = pm->extra_subflows < U8_MAX; + if (allow) + pm->extra_subflows++; spin_unlock_bh(&pm->lock); - return true; + return allow; } return false; } -- 2.43.0