@@ -938,8 +938,7 @@ static int udp_send_skb(struct sk_buff *skb, struct flowi4 *fl4,
kfree_skb(skb);
return -EINVAL;
}
- if (skb->ip_summed != CHECKSUM_PARTIAL || is_udplite ||
- dst_xfrm(skb_dst(skb))) {
+ if (is_udplite || dst_xfrm(skb_dst(skb))) {
kfree_skb(skb);
return -EIO;
}
@@ -357,6 +357,14 @@ struct sk_buff *__udp_gso_segment(struct sk_buff *gso_skb,
else
uh->check = gso_make_checksum(seg, ~check) ? : CSUM_MANGLED_0;
+ /* On the TX path, CHECKSUM_NONE and CHECKSUM_UNNECESSARY have the same
+ * meaning. However, check for bad offloads in the GSO stack expects the
+ * latter, if the checksum was calculated in software. To vouch for the
+ * segment skbs we actually need to set it on the gso_skb.
+ */
+ if (gso_skb->ip_summed == CHECKSUM_NONE)
+ gso_skb->ip_summed = CHECKSUM_UNNECESSARY;
+
/* update refcount for the packet */
if (copy_dtor) {
int delta = sum_truesize - gso_skb->truesize;
@@ -1257,8 +1257,7 @@ static int udp_v6_send_skb(struct sk_buff *skb, struct flowi6 *fl6,
kfree_skb(skb);
return -EINVAL;
}
- if (skb->ip_summed != CHECKSUM_PARTIAL || is_udplite ||
- dst_xfrm(skb_dst(skb))) {
+ if (is_udplite || dst_xfrm(skb_dst(skb))) {
kfree_skb(skb);
return -EIO;
}
Today sending a UDP GSO packet from a TUN device results in an EIO error: import fcntl, os, struct from socket import * TUNSETIFF = 0x400454CA IFF_TUN = 0x0001 IFF_NO_PI = 0x1000 UDP_SEGMENT = 103 tun_fd = os.open("/dev/net/tun", os.O_RDWR) ifr = struct.pack("16sH", b"tun0", IFF_TUN | IFF_NO_PI) fcntl.ioctl(tun_fd, TUNSETIFF, ifr) os.system("ip addr add 192.0.2.1/24 dev tun0") os.system("ip link set dev tun0 up") s = socket(AF_INET, SOCK_DGRAM) s.setsockopt(SOL_UDP, UDP_SEGMENT, 1200) s.sendto(b"x" * 3000, ("192.0.2.2", 9)) # EIO This is due to a check in the udp stack if the egress device offers checksum offload. TUN/TAP devices, by default, don't advertise this capability because it requires support from the TUN/TAP reader. However, the GSO stack has a software fallback for checksum calculation, which we can use. This way we don't force UDP_SEGMENT users to handle the EIO error and implement a segmentation fallback. Even if it means a potentially worse performance (see discussion in [1]). Lift the restriction so that user-space can use UDP_SEGMENT with any egress device. We also need to adjust the UDP GSO code to match the GSO stack expectation about ip_summed field, as set in commit 8d63bee643f1 ("net: avoid skb_warn_bad_offload false positives on UFO"). Otherwise we will hit the bad offload check. [1] https://lore.kernel.org/netdev/87jzqsld6q.fsf@cloudflare.com/ Fixes: bec1f6f69736 ("udp: generate gso with UDP_SEGMENT") Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com> --- net/ipv4/udp.c | 3 +-- net/ipv4/udp_offload.c | 8 ++++++++ net/ipv6/udp.c | 3 +-- 3 files changed, 10 insertions(+), 4 deletions(-)