lists.openwall.net   lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  linux-cve-announce  PHC 
Open Source and information security mailing list archives
 
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-Id: <20211115165346.122254948@linuxfoundation.org>
Date:   Mon, 15 Nov 2021 17:56:37 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Cyril Strejc <cyril.strejc@...da.cz>,
        Willem de Bruijn <willemb@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.10 072/575] net: multicast: calculate csum of looped-back and forwarded packets

From: Cyril Strejc <cyril.strejc@...da.cz>

[ Upstream commit 9122a70a6333705c0c35614ddc51c274ed1d3637 ]

During a testing of an user-space application which transmits UDP
multicast datagrams and utilizes multicast routing to send the UDP
datagrams out of defined network interfaces, I've found a multicast
router does not fill-in UDP checksum into locally produced, looped-back
and forwarded UDP datagrams, if an original output NIC the datagrams
are sent to has UDP TX checksum offload enabled.

The datagrams are sent malformed out of the NIC the datagrams have been
forwarded to.

It is because:

1. If TX checksum offload is enabled on the output NIC, UDP checksum
   is not calculated by kernel and is not filled into skb data.

2. dev_loopback_xmit(), which is called solely by
   ip_mc_finish_output(), sets skb->ip_summed = CHECKSUM_UNNECESSARY
   unconditionally.

3. Since 35fc92a9 ("[NET]: Allow forwarding of ip_summed except
   CHECKSUM_COMPLETE"), the ip_summed value is preserved during
   forwarding.

4. If ip_summed != CHECKSUM_PARTIAL, checksum is not calculated during
   a packet egress.

The minimum fix in dev_loopback_xmit():

1. Preserves skb->ip_summed CHECKSUM_PARTIAL. This is the
   case when the original output NIC has TX checksum offload enabled.
   The effects are:

     a) If the forwarding destination interface supports TX checksum
        offloading, the NIC driver is responsible to fill-in the
        checksum.

     b) If the forwarding destination interface does NOT support TX
        checksum offloading, checksums are filled-in by kernel before
        skb is submitted to the NIC driver.

     c) For local delivery, checksum validation is skipped as in the
        case of CHECKSUM_UNNECESSARY, thanks to skb_csum_unnecessary().

2. Translates ip_summed CHECKSUM_NONE to CHECKSUM_UNNECESSARY. It
   means, for CHECKSUM_NONE, the behavior is unmodified and is there
   to skip a looped-back packet local delivery checksum validation.

Signed-off-by: Cyril Strejc <cyril.strejc@...da.cz>
Reviewed-by: Willem de Bruijn <willemb@...gle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 include/net/udp.h | 5 +++--
 net/core/dev.c    | 3 ++-
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/include/net/udp.h b/include/net/udp.h
index 949ae14a54250..435cc009e6eaa 100644
--- a/include/net/udp.h
+++ b/include/net/udp.h
@@ -488,8 +488,9 @@ static inline struct sk_buff *udp_rcv_segment(struct sock *sk,
 	 * CHECKSUM_NONE in __udp_gso_segment. UDP GRO indeed builds partial
 	 * packets in udp_gro_complete_segment. As does UDP GSO, verified by
 	 * udp_send_skb. But when those packets are looped in dev_loopback_xmit
-	 * their ip_summed is set to CHECKSUM_UNNECESSARY. Reset in this
-	 * specific case, where PARTIAL is both correct and required.
+	 * their ip_summed CHECKSUM_NONE is changed to CHECKSUM_UNNECESSARY.
+	 * Reset in this specific case, where PARTIAL is both correct and
+	 * required.
 	 */
 	if (skb->pkt_type == PACKET_LOOPBACK)
 		skb->ip_summed = CHECKSUM_PARTIAL;
diff --git a/net/core/dev.c b/net/core/dev.c
index 6a4e0e3c59fec..e14294e9ba321 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3867,7 +3867,8 @@ int dev_loopback_xmit(struct net *net, struct sock *sk, struct sk_buff *skb)
 	skb_reset_mac_header(skb);
 	__skb_pull(skb, skb_network_offset(skb));
 	skb->pkt_type = PACKET_LOOPBACK;
-	skb->ip_summed = CHECKSUM_UNNECESSARY;
+	if (skb->ip_summed == CHECKSUM_NONE)
+		skb->ip_summed = CHECKSUM_UNNECESSARY;
 	WARN_ON(!skb_dst(skb));
 	skb_dst_force(skb);
 	netif_rx_ni(skb);
-- 
2.33.0



Powered by blists - more mailing lists

Powered by Openwall GNU/*/Linux Powered by OpenVZ