From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=95.215.58.196 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794212311; b=CGgFc+oksHF1R7jpV3/nPLZuq9K55RsEzM66zniQanu6ivnz6jigxrz3B02oxewPcVaR UiBV1YyILbb6luu0mVB5i1/8CqjN8id8v/ocpDAi53/VRrgbMmCqf7XUeVfxVwTv1MMdj 5dyFw61AQw/KOpNr3b65kM+fgJwsajKasnyOj5zeS59Jazx4DNl9GfJ5dh7Fr8yFKMGHB kUxs8mVvKA3ZL0Tbix/sW0NNFXawt5YeG2GFyHC32S8JX54UxRPCuwxMZZ0iXrk3QxwAt v2+m4mNOWUrc4ZjFmleR5zanVCI5nQ2HT/E5JdmjfB7+YalPSUFL9vRwxLmYDPOv7LA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794212311; h=DMARC-Filter:X-Envelope-To:DKIM-Signature:X-Envelope-To:Received: X-Mizu-Trace-ID:X-Migadu-Flow:From:Date:Subject:MIME-Version: Content-Type:Content-Transfer-Encoding:Message-Id:References: In-Reply-To:To:Cc:X-Mailer; bh=s1V/602Pvf6uE5BCQE9B8z2Cenl6Olf1l+jKmakHRg8=; b=Bms+9t7ey0v22VCbz2N+RGgAl4kZIjJ51IxCMNi3YXTdTsHilGRzTS59uRDx+8mVEGH3 tWmsu0CpbR0I68uCrqih0d+QJCgxQqpabLzPxYUXYuX5KZvHwPIRe550JqSCOSby6jqGQ SBgTQa3UhYRTLPAB+tliAg5H5PVSSsfVzhYaaE+RQeS3P3SYMmvHLfvx4Mf5dQMpHXlNL v6Q36ezTL3ZlPJSLu2A07BcYhbGDriSJHVtahcplr9Eet9TRpXxvDCriHnpDtJttU6RWz vPrsq5LT+EU6/FQ4qx7rwx9xDlD+94hMZbQo8FzeL9ymY2aakL7Nf5rPmnBVyQsxmPA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=BkOQTj7X; arc=none smtp.remote-ip=95.215.58.196 Received: from mta1.migadu.com (out-196.mta1.migadu.com [95.215.58.196]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 90E0A606A332 for ; Mon, 9 Nov 2026 08:18:30 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 90E0A606A332 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, unprotected) header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=BkOQTj7X X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=+uxdZdGdNJPaHe9dS43uJhHV3BwO0JbjvLd8aDJ6RQU=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1794212308; v=1; x=1794817108; b=BkOQTj7XinxkpwMPXbz0G/PIct5Z+LitNKtZcia8vb6+FWZ42bUxtjDP15HHYnqTM/hdglcQ yosH6a4eLAKqXGkLoP1KIc4QMzq+sFOX5VItDIReIyAAouJSK0QWBGy6TxC0bbFdaznrX6eWKfe oA7WWHrsQhhXuel4TMveGNAc= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 6fb67f112d4cb988; Mon, 09 Nov 2026 08:18:28 +0000 X-Mizu-Trace-ID: 6fb67f112d4cb988 X-Migadu-Flow: FLOW_OUT From: Qiliang Yuan Date: Mon, 09 Nov 2026 03:18:12 -0500 Subject: [PATCH net-next v3 1/4] ipv4: draw rt_genid from a sequence shared by all netns X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20261109-bug-net-netns-move-rcu-barrier-v3-1-6084b02610b3@linux.dev> References: <20261109-bug-net-netns-move-rcu-barrier-v3-0-6084b02610b3@linux.dev> In-Reply-To: <20261109-bug-net-netns-move-rcu-barrier-v3-0-6084b02610b3@linux.dev> To: "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , David Ahern , Ido Schimmel , Nikolay Aleksandrov Cc: Kuniyuki Iwashima , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Qiliang Yuan X-Mailer: b4 0.13.0 An IPv4 route records the rt_genid of the netns it was created in, and rt_is_expired() compares it with the rt_genid of the netns its device belongs to when the route is checked. Every netns starts its rt_genid at 0 and increments it on each cache flush, so different netns often hold the same value. When a device moves to another netns, routes cached through it remain usable until dst_dev_put() points them to blackhole_netdev. For a route using a nexthop object this happens in nexthop_free_rcu(), which free_fib_info_rcu() queues from inside an RCU callback, so the rcu_barrier() in __dev_change_net_namespace() does not wait for it. If the rt_genid of the new netns matches the cached one in that window, ipv4_dst_check() accepts the route and a socket in the old netns keeps sending through a device that now belongs to another netns. Take every rt_genid bump from one sequence shared by all netns, which never hands out 0, the value every netns starts with. Inserting a route bumps rt_genid, so the routes a netns caches carry values drawn from the sequence, which no other netns holds until it wraps after 2^32 bumps. Concurrent bumps of one netns can leave the older of two values, so rt_genid is no longer monotonic per netns. It is only compared for equality, so this costs at most an extra route lookup. A connected UDP socket in netns A caches a route through a nexthop object on a veth. The veth is moved to netns B and brought up with one RTM_NEWLINK, then the socket sends 200000 datagrams. B's rt_genid is bumped 0 to 20 times before the move, 63 trials: before after trials sending after move 3 0 datagrams sent after move 3132 0 Fixes: 4c7e8084fd46 ("ipv4: Plumb support for nexthop object in a fib_info") Signed-off-by: Qiliang Yuan Reviewed-by: Kuniyuki Iwashima --- include/net/net_namespace.h | 5 +---- net/ipv4/route.c | 21 +++++++++++++++++++++ 2 files changed, 22 insertions(+), 4 deletions(-) diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h index c29a22ca178fa..140858a2fe6d4 100644 --- a/include/net/net_namespace.h +++ b/include/net/net_namespace.h @@ -557,10 +557,7 @@ static inline int rt_genid_ipv6(const struct net *net) } #endif -static inline void rt_genid_bump_ipv4(struct net *net) -{ - atomic_inc(&net->ipv4.rt_genid); -} +void rt_genid_bump_ipv4(struct net *net); extern void (*__fib6_flush_trees)(struct net *net); static inline void rt_genid_bump_ipv6(struct net *net) diff --git a/net/ipv4/route.c b/net/ipv4/route.c index d0a5f6d77094c..16d470ab50142 100644 --- a/net/ipv4/route.c +++ b/net/ipv4/route.c @@ -393,6 +393,27 @@ static inline int ip_rt_proc_init(void) } #endif /* CONFIG_PROC_FS */ +/* + * Draw rt_genid bumps from one sequence shared by all netns. A route keeps + * the genid of the netns it was created in, and is checked against the netns + * its device is in now, so distinct values make that check fail once the + * device has moved. Every netns starts at 0, which the sequence never hands + * out, and inserting a route bumps the genid, so cached routes carry values + * drawn from the sequence. + */ +static atomic_t rt_genid_seq; + +void rt_genid_bump_ipv4(struct net *net) +{ + int genid; + + do { + genid = atomic_inc_return(&rt_genid_seq); + } while (!genid); + atomic_set(&net->ipv4.rt_genid, genid); +} +EXPORT_SYMBOL_GPL(rt_genid_bump_ipv4); + static inline bool rt_is_expired(const struct rtable *rth) { bool res; -- 2.43.0