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Message-ID: <Z5cgWh/6bRQm9vVU@debian.debian>
Date: Sun, 26 Jan 2025 21:57:46 -0800
From: Yan Zhai <yan@...udflare.com>
To: netdev@...r.kernel.org
Cc: Willem de Bruijn <willemdebruijn.kernel@...il.com>,
"David S. Miller" <davem@...emloft.net>,
David Ahern <dsahern@...nel.org>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
Simon Horman <horms@...nel.org>, Shuah Khan <shuah@...nel.org>,
Josh Hunt <johunt@...mai.com>,
Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-kselftest@...r.kernel.org
Subject: [PATCH] udp: gso: fix MTU check for small packets
Commit 4094871db1d6 ("udp: only do GSO if # of segs > 1") avoided GSO
for small packets. But the kernel currently dismisses GSO requests only
after checking MTU on gso_size. This means any packets, regardless of
their payload sizes, would be dropped when MTU is smaller than requested
gso_size. Meanwhile, EINVAL would be returned in this case, making it
very misleading to debug.
Ideally, do not check any GSO related constraints when payload size is
smaller than requested gso_size, and return EMSGSIZE on MTU check
failure consistently for all packets to ease debugging.
Fixes: 4094871db1d6 ("udp: only do GSO if # of segs > 1")
Signed-off-by: Yan Zhai <yan@...udflare.com>
---
net/ipv4/udp.c | 18 ++++++++----------
net/ipv6/udp.c | 18 ++++++++----------
tools/testing/selftests/net/udpgso.c | 14 ++++++++++++++
3 files changed, 30 insertions(+), 20 deletions(-)
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index c472c9a57cf6..9aed1b4a871f 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1137,13 +1137,13 @@ static int udp_send_skb(struct sk_buff *skb, struct flowi4 *fl4,
uh->len = htons(len);
uh->check = 0;
- if (cork->gso_size) {
+ if (cork->gso_size && datalen > cork->gso_size) {
const int hlen = skb_network_header_len(skb) +
sizeof(struct udphdr);
if (hlen + cork->gso_size > cork->fragsize) {
kfree_skb(skb);
- return -EINVAL;
+ return -EMSGSIZE;
}
if (datalen > cork->gso_size * UDP_MAX_SEGMENTS) {
kfree_skb(skb);
@@ -1158,15 +1158,13 @@ static int udp_send_skb(struct sk_buff *skb, struct flowi4 *fl4,
return -EIO;
}
- if (datalen > cork->gso_size) {
- skb_shinfo(skb)->gso_size = cork->gso_size;
- skb_shinfo(skb)->gso_type = SKB_GSO_UDP_L4;
- skb_shinfo(skb)->gso_segs = DIV_ROUND_UP(datalen,
- cork->gso_size);
+ skb_shinfo(skb)->gso_size = cork->gso_size;
+ skb_shinfo(skb)->gso_type = SKB_GSO_UDP_L4;
+ skb_shinfo(skb)->gso_segs = DIV_ROUND_UP(datalen,
+ cork->gso_size);
- /* Don't checksum the payload, skb will get segmented */
- goto csum_partial;
- }
+ /* Don't checksum the payload, skb will get segmented */
+ goto csum_partial;
}
if (is_udplite) /* UDP-Lite */
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index 6671daa67f4f..6cdc8ce4c6f9 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -1385,13 +1385,13 @@ static int udp_v6_send_skb(struct sk_buff *skb, struct flowi6 *fl6,
uh->len = htons(len);
uh->check = 0;
- if (cork->gso_size) {
+ if (cork->gso_size && datalen > cork->gso_size) {
const int hlen = skb_network_header_len(skb) +
sizeof(struct udphdr);
if (hlen + cork->gso_size > cork->fragsize) {
kfree_skb(skb);
- return -EINVAL;
+ return -EMSGSIZE;
}
if (datalen > cork->gso_size * UDP_MAX_SEGMENTS) {
kfree_skb(skb);
@@ -1406,15 +1406,13 @@ static int udp_v6_send_skb(struct sk_buff *skb, struct flowi6 *fl6,
return -EIO;
}
- if (datalen > cork->gso_size) {
- skb_shinfo(skb)->gso_size = cork->gso_size;
- skb_shinfo(skb)->gso_type = SKB_GSO_UDP_L4;
- skb_shinfo(skb)->gso_segs = DIV_ROUND_UP(datalen,
- cork->gso_size);
+ skb_shinfo(skb)->gso_size = cork->gso_size;
+ skb_shinfo(skb)->gso_type = SKB_GSO_UDP_L4;
+ skb_shinfo(skb)->gso_segs = DIV_ROUND_UP(datalen,
+ cork->gso_size);
- /* Don't checksum the payload, skb will get segmented */
- goto csum_partial;
- }
+ /* Don't checksum the payload, skb will get segmented */
+ goto csum_partial;
}
if (is_udplite)
diff --git a/tools/testing/selftests/net/udpgso.c b/tools/testing/selftests/net/udpgso.c
index 3f2fca02fec5..fb73f1c331fb 100644
--- a/tools/testing/selftests/net/udpgso.c
+++ b/tools/testing/selftests/net/udpgso.c
@@ -102,6 +102,13 @@ struct testcase testcases_v4[] = {
.gso_len = CONST_MSS_V4,
.r_num_mss = 1,
},
+ {
+ /* datalen <= MSS < gso_len: will fall back to no GSO */
+ .tlen = CONST_MSS_V4,
+ .gso_len = CONST_MSS_V4 + 1,
+ .r_num_mss = 0,
+ .r_len_last = CONST_MSS_V4,
+ },
{
/* send a single MSS + 1B */
.tlen = CONST_MSS_V4 + 1,
@@ -205,6 +212,13 @@ struct testcase testcases_v6[] = {
.gso_len = CONST_MSS_V6,
.r_num_mss = 1,
},
+ {
+ /* datalen <= MSS < gso_len: will fall back to no GSO */
+ .tlen = CONST_MSS_V6,
+ .gso_len = CONST_MSS_V6 + 1,
+ .r_num_mss = 0,
+ .r_len_last = CONST_MSS_V6,
+ },
{
/* send a single MSS + 1B */
.tlen = CONST_MSS_V6 + 1,
--
2.30.2
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