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79fce42404
Fixes some corner cases regarding segmenting packets that were assembled by GRO. Signed-off-by: Felix Fietkau <nbd@nbd.name>
95 lines
3.4 KiB
Diff
95 lines
3.4 KiB
Diff
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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