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 ACE162F28; Mon, 10 Mar 2025 18:18:01 +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=1741630681; cv=none; b=IMEcQV9g9RPb8cpVNaxxGutcjo2YcGj+B8ycUFGL1UsdP+tWVU0tLZXDGaXYul2tdleoze7a0X1Twr+0SwwL19qC439zGqCaiJH92ssYIsnkhb6w3+rO1C2sjmnvrcfsZEWhiikRY6SnseEpdasmT9Bx1ZWuiu3N4PtjKSlQRUQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741630681; c=relaxed/simple; bh=BLMmwmwh5Cz+NVNca2+wY5iZ4f6OFv+iQkuRhTEClBw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=aavSxlOB5LsAPCbm0Czzao7W2qN9XsKFvMuQxMc+nuo52YAeixHlqp97jwKQwLZ8Og4M7VcSqKN6359bAD1XjBCieZz5laJ38Ud2Pe2JaD2pzHfjBRdiFZ+5V7dCLobFQYD6Q/TRIQ0wjM6H9Db8KTsSjdcUhkSS0UU+d/9J/WE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=Os/Yvz9T; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="Os/Yvz9T" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 336FBC4CEE5; Mon, 10 Mar 2025 18:18:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1741630681; bh=BLMmwmwh5Cz+NVNca2+wY5iZ4f6OFv+iQkuRhTEClBw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Os/Yvz9Tnx9NeRy8J8Yfg/QkVBQgdEWIDUZ+v84iJrIoiEqO3XX5Z25ATuNaV9fEu RulfJxG2Se7ytkho1X9I86Tz7CFBQtnZpc84q85asWnEM6xBUWCfH0SkotfoknO1fM BdMrDSwyGrqAkEDKmZz2dt6mDIjJI38kH9l6tW3E= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Florian Meister , Ido Schimmel , Eric Dumazet , Jakub Kicinski , Sasha Levin Subject: [PATCH 5.15 499/620] net: loopback: Avoid sending IP packets without an Ethernet header Date: Mon, 10 Mar 2025 18:05:45 +0100 Message-ID: <20250310170605.266217970@linuxfoundation.org> X-Mailer: git-send-email 2.48.1 In-Reply-To: <20250310170545.553361750@linuxfoundation.org> References: <20250310170545.553361750@linuxfoundation.org> User-Agent: quilt/0.68 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 5.15-stable review patch. If anyone has any objections, please let me know. ------------------ From: Ido Schimmel [ Upstream commit 0e4427f8f587c4b603475468bb3aee9418574893 ] After commit 22600596b675 ("ipv4: give an IPv4 dev to blackhole_netdev") IPv4 neighbors can be constructed on the blackhole net device, but they are constructed with an output function (neigh_direct_output()) that simply calls dev_queue_xmit(). The latter will transmit packets via 'skb->dev' which might not be the blackhole net device if dst_dev_put() switched 'dst->dev' to the blackhole net device while another CPU was using the dst entry in ip_output(), but after it already initialized 'skb->dev' from 'dst->dev'. Specifically, the following can happen: CPU1 CPU2 udp_sendmsg(sk1) udp_sendmsg(sk2) udp_send_skb() [...] ip_output() skb->dev = skb_dst(skb)->dev dst_dev_put() dst->dev = blackhole_netdev ip_finish_output2() resolves neigh on dst->dev neigh_output() neigh_direct_output() dev_queue_xmit() This will result in IPv4 packets being sent without an Ethernet header via a valid net device: tcpdump: verbose output suppressed, use -v[v]... for full protocol decode listening on enp9s0, link-type EN10MB (Ethernet), snapshot length 262144 bytes 22:07:02.329668 20:00:40:11:18:fb > 45:00:00:44:f4:94, ethertype Unknown (0x58c6), length 68: 0x0000: 8dda 74ca f1ae ca6c ca6c 0098 969c 0400 ..t....l.l...... 0x0010: 0000 4730 3f18 6800 0000 0000 0000 9971 ..G0?.h........q 0x0020: c4c9 9055 a157 0a70 9ead bf83 38ca ab38 ...U.W.p....8..8 0x0030: 8add ab96 e052 .....R Fix by making sure that neighbors are constructed on top of the blackhole net device with an output function that simply consumes the packets, in a similar fashion to dst_discard_out() and blackhole_netdev_xmit(). Fixes: 8d7017fd621d ("blackhole_netdev: use blackhole_netdev to invalidate dst entries") Fixes: 22600596b675 ("ipv4: give an IPv4 dev to blackhole_netdev") Reported-by: Florian Meister Closes: https://lore.kernel.org/netdev/20250210084931.23a5c2e4@hermes.local/ Signed-off-by: Ido Schimmel Reviewed-by: Eric Dumazet Link: https://patch.msgid.link/20250220072559.782296-1-idosch@nvidia.com Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin --- drivers/net/loopback.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/drivers/net/loopback.c b/drivers/net/loopback.c index 498e5c8013efb..0160a4f57ce92 100644 --- a/drivers/net/loopback.c +++ b/drivers/net/loopback.c @@ -243,8 +243,22 @@ static netdev_tx_t blackhole_netdev_xmit(struct sk_buff *skb, return NETDEV_TX_OK; } +static int blackhole_neigh_output(struct neighbour *n, struct sk_buff *skb) +{ + kfree_skb(skb); + return 0; +} + +static int blackhole_neigh_construct(struct net_device *dev, + struct neighbour *n) +{ + n->output = blackhole_neigh_output; + return 0; +} + static const struct net_device_ops blackhole_netdev_ops = { .ndo_start_xmit = blackhole_netdev_xmit, + .ndo_neigh_construct = blackhole_neigh_construct, }; /* This is a dst-dummy device used specifically for invalidated -- 2.39.5