From nobody Sat Sep 5 05:48:51 2026 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: quoted-printable Content-Type: text/plain; charset="utf-8" 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 *ms= k) =20 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 =3D pm->extra_subflows < U8_MAX; + if (allow) + pm->extra_subflows++; spin_unlock_bh(&pm->lock); - return true; + return allow; } return false; } --=20 2.43.0 From nobody Sat Sep 5 05:48:51 2026 Received: from mta1.migadu.com (out-251.mta1.migadu.com [95.215.58.251]) (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 A6AFF3CAA59 for ; Mon, 31 Aug 2026 09:32:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.251 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788168759; cv=none; b=brSDh9gkcjtlYdPxbz29uEskkEX3mhsYlUut/KIaNnLVMFM+x/1BCn0T9MHp/AIWgsZMHKMmaIv8yDYMNEGhv4lXwD+tlj7kzyZ8JDgZMzELN0F3LzZoOQCn4tGFFQCNRuyEGA7ajmtOzb/rfyWX8Mv4phBcT1HOPsYeyO4tVU8= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788168759; c=relaxed/simple; bh=ws/E51gGgS3vg/9PEA6emAwTLsLkVDJZ6mM04VkDJ9s=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Xv+1fcZl0J3OMqklRcHRIP+7aKecpHm9m4/TOobWJXsoMlGW+QM13hMUclNeVxEhNl4xWD/z0oefgV2WGx2ppeAiEerZObJsDsLS49gzReLY6kvG2driicHvUXplVlZwxkoFDIUvdul4xB1s/+cx09RbFmEunLU9GBhrMaveTN8= 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=YSDUlnCH; arc=none smtp.client-ip=95.215.58.251 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="YSDUlnCH" X-Envelope-To: mptcp@lists.linux.dev DKIM-Signature: a=rsa-sha256; bh=ws/E51gGgS3vg/9PEA6emAwTLsLkVDJZ6mM04VkDJ9s=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1788168755; v=1; x=1788773555; b=YSDUlnCHrcBcjDPgp6JxPQ3rqmL1rWdT9dvOAkFcT2x1sMIvn2heDBMZAqA6n5C/EmeHgcsK xQ/jQlduBYIiUstHSLz9qW5pA9fBoY+pUlQq1c9E6U3rUwy/DOMipZtRAvpOoTTgrS3vpotlQFE JBrc8pZt0zzZQNE1BfBCTmq0= X-Envelope-To: mptcp@lists.linux.dev Received: by smtp.migadu.com with ESMTPS id 5234ddb29e01091d; Mon, 31 Aug 2026 09:32:35 +0000 X-Mizu-Trace-ID: 5234ddb29e01091d 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 2/2] mptcp: pm: skip extra_subflows accounting on disconnected msk Date: Mon, 31 Aug 2026 17:32:06 +0800 Message-ID: <20260831093206.689827-3-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: quoted-printable Content-Type: text/plain; charset="utf-8" From: Tao Cui The WARN_ON_ONCE() guards added to the extra_subflows decrement sites turn out to be reachable: mptcp_pm_data_reset() zeroes the counter with only the msk socket lock held, while an MP_JOIN subflow can still sit in msk->join_list, its reference already accounted by mptcp_pm_allow_new_subflow() under pm->lock. If the socket gets disconnected(AF_UNSPEC) in that window, mptcp_pm_data_reset() zeroes the counter, and the join list is flushed later at release_sock() time: the leftover subflow then reaches mptcp_pm_subflow_check_next() (or __mptcp_pm_close_subflow() for kernel PM sockets) with the counter already at 0, firing the warning. On panic_on_warn kernels this is a remotely triggerable panic, which is worse than the silent wrap the guards replaced. Skip the PM accounting when the msk is already in TCP_CLOSE: in the scenario above the state is set before the counters are cleared, and once the msk is closed the accounting is not relevant anymore. Keep a clamp and a rate-limited pr_warn() on the decrement sites instead, to leave a trace of any imbalance we would still not know about. Fixes: e99c1ca89071 ("mptcp: pm: add WARN_ON_ONCE guards on extra_subflows = underflow") Link: https://github.com/multipath-tcp/mptcp_net-next/issues/629 Suggested-by: Matthieu Baerts Signed-off-by: Tao Cui --- net/mptcp/pm.c | 11 ++++++++++- net/mptcp/protocol.h | 14 ++++++++++++-- 2 files changed, 22 insertions(+), 3 deletions(-) diff --git a/net/mptcp/pm.c b/net/mptcp/pm.c index 3990f6775723..1760f4c51b62 100644 --- a/net/mptcp/pm.c +++ b/net/mptcp/pm.c @@ -676,9 +676,18 @@ void mptcp_pm_subflow_check_next(struct mptcp_sock *ms= k, update_subflows =3D subflow->request_join || subflow->mp_join; if (mptcp_pm_is_userspace(msk)) { if (update_subflows) { + /* The PM counters have already been cleared if the + * msk got disconnected while this subflow was still + * queued in the join list + */ + if (inet_sk_state_load(sk) =3D=3D TCP_CLOSE) + return; spin_lock_bh(&pm->lock); - if (!WARN_ON_ONCE(pm->extra_subflows =3D=3D 0)) + if (likely(pm->extra_subflows)) pm->extra_subflows--; + else + pr_warn_ratelimited("extra_subflows underflow, msk=3D%p\n", + msk); spin_unlock_bh(&pm->lock); } return; diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h index 06a107d4e839..f5dbafaf4551 100644 --- a/net/mptcp/protocol.h +++ b/net/mptcp/protocol.h @@ -1252,8 +1252,18 @@ u8 mptcp_pm_get_limit_extra_subflows(const struct mp= tcp_sock *msk); /* called under PM lock */ static inline void __mptcp_pm_close_subflow(struct mptcp_sock *msk) { - if (!WARN_ON_ONCE(msk->pm.extra_subflows =3D=3D 0) && - --msk->pm.extra_subflows < mptcp_pm_get_limit_extra_subflows(msk)) + /* The PM counters have already been cleared if the msk got + * disconnected while this subflow was still queued in the + * join list + */ + if (inet_sk_state_load((struct sock *)msk) =3D=3D TCP_CLOSE) + return; + + if (unlikely(msk->pm.extra_subflows =3D=3D 0)) { + pr_warn_ratelimited("extra_subflows underflow, msk=3D%p\n", msk); + return; + } + if (--msk->pm.extra_subflows < mptcp_pm_get_limit_extra_subflows(msk)) WRITE_ONCE(msk->pm.accept_subflow, true); } =20 --=20 2.43.0