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kernel: backport upstream GSO improvements
Fixes some corner cases regarding segmenting packets that were assembled by GRO. Signed-off-by: Felix Fietkau <nbd@nbd.name>
This commit is contained in:
Felix Fietkau
parent
e497c975d3
commit
79fce42404
@ -0,0 +1,94 @@
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From: Jakub Sitnicki <jakub@cloudflare.com>
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Date: Wed, 26 Jun 2024 19:51:26 +0200
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Subject: [PATCH] udp: Allow GSO transmit from devices with no checksum offload
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Today sending a UDP GSO packet from a TUN device results in an EIO error:
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import fcntl, os, struct
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from socket import *
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TUNSETIFF = 0x400454CA
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IFF_TUN = 0x0001
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IFF_NO_PI = 0x1000
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UDP_SEGMENT = 103
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tun_fd = os.open("/dev/net/tun", os.O_RDWR)
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ifr = struct.pack("16sH", b"tun0", IFF_TUN | IFF_NO_PI)
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fcntl.ioctl(tun_fd, TUNSETIFF, ifr)
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os.system("ip addr add 192.0.2.1/24 dev tun0")
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os.system("ip link set dev tun0 up")
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s = socket(AF_INET, SOCK_DGRAM)
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s.setsockopt(SOL_UDP, UDP_SEGMENT, 1200)
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s.sendto(b"x" * 3000, ("192.0.2.2", 9)) # EIO
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This is due to a check in the udp stack if the egress device offers
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checksum offload. While TUN/TAP devices, by default, don't advertise this
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capability because it requires support from the TUN/TAP reader.
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However, the GSO stack has a software fallback for checksum calculation,
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which we can use. This way we don't force UDP_SEGMENT users to handle the
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EIO error and implement a segmentation fallback.
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Lift the restriction so that UDP_SEGMENT can be used with any egress
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device. We also need to adjust the UDP GSO code to match the GSO stack
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expectation about ip_summed field, as set in commit 8d63bee643f1 ("net:
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avoid skb_warn_bad_offload false positives on UFO"). Otherwise we will hit
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the bad offload check.
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Users should, however, expect a potential performance impact when
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batch-sending packets with UDP_SEGMENT without checksum offload on the
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egress device. In such case the packet payload is read twice: first during
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the sendmsg syscall when copying data from user memory, and then in the GSO
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stack for checksum computation. This double memory read can be less
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efficient than a regular sendmsg where the checksum is calculated during
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the initial data copy from user memory.
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Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
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Reviewed-by: Willem de Bruijn <willemb@google.com>
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Link: https://patch.msgid.link/20240626-linux-udpgso-v2-1-422dfcbd6b48@cloudflare.com
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Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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---
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--- a/net/ipv4/udp.c
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+++ b/net/ipv4/udp.c
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@@ -942,8 +942,7 @@ static int udp_send_skb(struct sk_buff *
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kfree_skb(skb);
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return -EINVAL;
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}
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- if (skb->ip_summed != CHECKSUM_PARTIAL || is_udplite ||
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- dst_xfrm(skb_dst(skb))) {
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+ if (is_udplite || dst_xfrm(skb_dst(skb))) {
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kfree_skb(skb);
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return -EIO;
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}
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--- a/net/ipv4/udp_offload.c
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+++ b/net/ipv4/udp_offload.c
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@@ -357,6 +357,14 @@ struct sk_buff *__udp_gso_segment(struct
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else
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uh->check = gso_make_checksum(seg, ~check) ? : CSUM_MANGLED_0;
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+ /* On the TX path, CHECKSUM_NONE and CHECKSUM_UNNECESSARY have the same
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+ * meaning. However, check for bad offloads in the GSO stack expects the
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+ * latter, if the checksum was calculated in software. To vouch for the
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+ * segment skbs we actually need to set it on the gso_skb.
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+ */
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+ if (gso_skb->ip_summed == CHECKSUM_NONE)
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+ gso_skb->ip_summed = CHECKSUM_UNNECESSARY;
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+
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/* update refcount for the packet */
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if (copy_dtor) {
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int delta = sum_truesize - gso_skb->truesize;
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--- a/net/ipv6/udp.c
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+++ b/net/ipv6/udp.c
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@@ -1261,8 +1261,7 @@ static int udp_v6_send_skb(struct sk_buf
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kfree_skb(skb);
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return -EINVAL;
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}
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- if (skb->ip_summed != CHECKSUM_PARTIAL || is_udplite ||
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- dst_xfrm(skb_dst(skb))) {
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+ if (is_udplite || dst_xfrm(skb_dst(skb))) {
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kfree_skb(skb);
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return -EIO;
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}
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@ -0,0 +1,69 @@
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From: Jakub Sitnicki <jakub@cloudflare.com>
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Date: Thu, 8 Aug 2024 11:56:21 +0200
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Subject: [PATCH] net: Make USO depend on CSUM offload
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UDP segmentation offload inherently depends on checksum offload. It should
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not be possible to disable checksum offload while leaving USO enabled.
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Enforce this dependency in code.
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There is a single tx-udp-segmentation feature flag to indicate support for
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both IPv4/6, hence the devices wishing to support USO must offer checksum
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offload for both IP versions.
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Fixes: 10154dbded6d ("udp: Allow GSO transmit from devices with no checksum offload")
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Suggested-by: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
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Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
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Reviewed-by: Willem de Bruijn <willemb@google.com>
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Link: https://patch.msgid.link/20240808-udp-gso-egress-from-tunnel-v4-1-f5c5b4149ab9@cloudflare.com
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Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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---
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--- a/net/core/dev.c
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+++ b/net/core/dev.c
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@@ -9751,6 +9751,15 @@ static void netdev_sync_lower_features(s
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}
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}
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+static bool netdev_has_ip_or_hw_csum(netdev_features_t features)
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+{
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+ netdev_features_t ip_csum_mask = NETIF_F_IP_CSUM | NETIF_F_IPV6_CSUM;
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+ bool ip_csum = (features & ip_csum_mask) == ip_csum_mask;
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+ bool hw_csum = features & NETIF_F_HW_CSUM;
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+
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+ return ip_csum || hw_csum;
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+}
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+
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static netdev_features_t netdev_fix_features(struct net_device *dev,
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netdev_features_t features)
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{
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@@ -9832,15 +9841,9 @@ static netdev_features_t netdev_fix_feat
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features &= ~NETIF_F_LRO;
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}
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- if (features & NETIF_F_HW_TLS_TX) {
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- bool ip_csum = (features & (NETIF_F_IP_CSUM | NETIF_F_IPV6_CSUM)) ==
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- (NETIF_F_IP_CSUM | NETIF_F_IPV6_CSUM);
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- bool hw_csum = features & NETIF_F_HW_CSUM;
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-
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- if (!ip_csum && !hw_csum) {
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- netdev_dbg(dev, "Dropping TLS TX HW offload feature since no CSUM feature.\n");
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- features &= ~NETIF_F_HW_TLS_TX;
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- }
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+ if ((features & NETIF_F_HW_TLS_TX) && !netdev_has_ip_or_hw_csum(features)) {
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+ netdev_dbg(dev, "Dropping TLS TX HW offload feature since no CSUM feature.\n");
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+ features &= ~NETIF_F_HW_TLS_TX;
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}
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if ((features & NETIF_F_HW_TLS_RX) && !(features & NETIF_F_RXCSUM)) {
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@@ -9848,6 +9851,11 @@ static netdev_features_t netdev_fix_feat
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features &= ~NETIF_F_HW_TLS_RX;
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}
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+ if ((features & NETIF_F_GSO_UDP_L4) && !netdev_has_ip_or_hw_csum(features)) {
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+ netdev_dbg(dev, "Dropping USO feature since no CSUM feature.\n");
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+ features &= ~NETIF_F_GSO_UDP_L4;
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+ }
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+
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return features;
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}
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@ -0,0 +1,86 @@
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From: Jakub Sitnicki <jakub@cloudflare.com>
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Date: Thu, 8 Aug 2024 11:56:22 +0200
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Subject: [PATCH] udp: Fall back to software USO if IPv6 extension headers are
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present
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In commit 10154dbded6d ("udp: Allow GSO transmit from devices with no
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checksum offload") we have intentionally allowed UDP GSO packets marked
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CHECKSUM_NONE to pass to the GSO stack, so that they can be segmented and
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checksummed by a software fallback when the egress device lacks these
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features.
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What was not taken into consideration is that a CHECKSUM_NONE skb can be
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handed over to the GSO stack also when the egress device advertises the
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tx-udp-segmentation / NETIF_F_GSO_UDP_L4 feature.
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This will happen when there are IPv6 extension headers present, which we
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check for in __ip6_append_data(). Syzbot has discovered this scenario,
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producing a warning as below:
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ip6tnl0: caps=(0x00000006401d7869, 0x00000006401d7869)
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WARNING: CPU: 0 PID: 5112 at net/core/dev.c:3293 skb_warn_bad_offload+0x166/0x1a0 net/core/dev.c:3291
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Modules linked in:
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CPU: 0 PID: 5112 Comm: syz-executor391 Not tainted 6.10.0-rc7-syzkaller-01603-g80ab5445da62 #0
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Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/07/2024
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RIP: 0010:skb_warn_bad_offload+0x166/0x1a0 net/core/dev.c:3291
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[...]
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Call Trace:
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<TASK>
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__skb_gso_segment+0x3be/0x4c0 net/core/gso.c:127
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skb_gso_segment include/net/gso.h:83 [inline]
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validate_xmit_skb+0x585/0x1120 net/core/dev.c:3661
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__dev_queue_xmit+0x17a4/0x3e90 net/core/dev.c:4415
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neigh_output include/net/neighbour.h:542 [inline]
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ip6_finish_output2+0xffa/0x1680 net/ipv6/ip6_output.c:137
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ip6_finish_output+0x41e/0x810 net/ipv6/ip6_output.c:222
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ip6_send_skb+0x112/0x230 net/ipv6/ip6_output.c:1958
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udp_v6_send_skb+0xbf5/0x1870 net/ipv6/udp.c:1292
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udpv6_sendmsg+0x23b3/0x3270 net/ipv6/udp.c:1588
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sock_sendmsg_nosec net/socket.c:730 [inline]
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__sock_sendmsg+0xef/0x270 net/socket.c:745
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____sys_sendmsg+0x525/0x7d0 net/socket.c:2585
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___sys_sendmsg net/socket.c:2639 [inline]
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__sys_sendmmsg+0x3b2/0x740 net/socket.c:2725
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__do_sys_sendmmsg net/socket.c:2754 [inline]
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__se_sys_sendmmsg net/socket.c:2751 [inline]
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__x64_sys_sendmmsg+0xa0/0xb0 net/socket.c:2751
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do_syscall_x64 arch/x86/entry/common.c:52 [inline]
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do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
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entry_SYSCALL_64_after_hwframe+0x77/0x7f
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[...]
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</TASK>
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We are hitting the bad offload warning because when an egress device is
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capable of handling segmentation offload requested by
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skb_shinfo(skb)->gso_type, the chain of gso_segment callbacks won't produce
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any segment skbs and return NULL. See the skb_gso_ok() branch in
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{__udp,tcp,sctp}_gso_segment helpers.
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To fix it, force a fallback to software USO when processing a packet with
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IPv6 extension headers, since we don't know if these can checksummed by
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all devices which offer USO.
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Fixes: 10154dbded6d ("udp: Allow GSO transmit from devices with no checksum offload")
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Reported-by: syzbot+e15b7e15b8a751a91d9a@syzkaller.appspotmail.com
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Closes: https://lore.kernel.org/all/000000000000e1609a061d5330ce@google.com/
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Reviewed-by: Willem de Bruijn <willemb@google.com>
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Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
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Link: https://patch.msgid.link/20240808-udp-gso-egress-from-tunnel-v4-2-f5c5b4149ab9@cloudflare.com
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Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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---
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--- a/net/ipv4/udp_offload.c
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+++ b/net/ipv4/udp_offload.c
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@@ -278,6 +278,12 @@ struct sk_buff *__udp_gso_segment(struct
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if (gso_skb->len <= sizeof(*uh) + mss)
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return ERR_PTR(-EINVAL);
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+ /* We don't know if egress device can segment and checksum the packet
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+ * when IPv6 extension headers are present. Fall back to software GSO.
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+ */
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+ if (gso_skb->ip_summed != CHECKSUM_PARTIAL)
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+ features &= ~(NETIF_F_GSO_UDP_L4 | NETIF_F_CSUM_MASK);
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+
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if (skb_gso_ok(gso_skb, features | NETIF_F_GSO_ROBUST)) {
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/* Packet is from an untrusted source, reset gso_segs. */
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skb_shinfo(gso_skb)->gso_segs = DIV_ROUND_UP(gso_skb->len - sizeof(*uh),
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@ -379,7 +379,7 @@ Signe-off-by: Felix Fietkau <nbd@nbd.name>
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skb_shinfo(skb)->gso_type |= SKB_GSO_TCPV4;
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--- a/net/ipv4/udp_offload.c
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+++ b/net/ipv4/udp_offload.c
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@@ -433,33 +433,6 @@ out:
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@@ -447,33 +447,6 @@ out:
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return segs;
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}
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