From: Kyle Zeng <kylebot@openai.com>
To: netdev@vger.kernel.org
Cc: Aaron Conole <aconole@redhat.com>,
Eelco Chaudron <echaudro@redhat.com>,
Ilya Maximets <i.maximets@ovn.org>,
Kyle Zeng <kylebot@openai.com>,
stable@vger.kernel.org
Subject: [PATCH net] openvswitch: fix GSO userspace truncation underflow
Date: Tue, 7 Jul 2026 15:16:35 -0700 [thread overview]
Message-ID: <20260707221635.27489-1-kylebot@openai.com> (raw)
OVS_ACTION_ATTR_TRUNC currently stores a delta from the original skb
length in OVS_CB(skb)->cutlen. When a later userspace action segments a
GSO skb, queue_gso_packets() reuses that delta for each smaller segment.
A segment can then reach queue_userspace_packet() with cutlen greater
than skb->len, underflowing the length passed to skb_zerocopy().
Store the maximum preserved length instead and bound each consumer
against the current skb length. Use U32_MAX as the no-truncation
sentinel so the value remains valid if skb geometry changes before a
consumer handles it.
Fixes: f2a4d086ed4c ("openvswitch: Add packet truncation support.")
Cc: stable@vger.kernel.org
Assisted-by: Codex:gpt-5.5
Signed-off-by: Kyle Zeng <kylebot@openai.com>
---
net/openvswitch/actions.c | 19 +++++++------------
net/openvswitch/datapath.c | 25 ++++++++++++++-----------
net/openvswitch/datapath.h | 2 +-
net/openvswitch/vport.c | 2 +-
4 files changed, 23 insertions(+), 25 deletions(-)
diff --git a/net/openvswitch/actions.c b/net/openvswitch/actions.c
index 140388a18ae0..513fca6a8e8a 100644
--- a/net/openvswitch/actions.c
+++ b/net/openvswitch/actions.c
@@ -837,12 +837,8 @@ static void do_output(struct datapath *dp, struct sk_buff *skb, int out_port,
u16 mru = OVS_CB(skb)->mru;
u32 cutlen = OVS_CB(skb)->cutlen;
- if (unlikely(cutlen > 0)) {
- if (skb->len - cutlen > ovs_mac_header_len(key))
- pskb_trim(skb, skb->len - cutlen);
- else
- pskb_trim(skb, ovs_mac_header_len(key));
- }
+ if (unlikely(cutlen < skb->len))
+ pskb_trim(skb, max(cutlen, ovs_mac_header_len(key)));
if (likely(!mru ||
(skb->len <= mru + vport->dev->hard_header_len))) {
@@ -1234,7 +1230,7 @@ static void execute_psample(struct datapath *dp, struct sk_buff *skb,
psample_group.net = ovs_dp_get_net(dp);
md.in_ifindex = OVS_CB(skb)->input_vport->dev->ifindex;
- md.trunc_size = skb->len - OVS_CB(skb)->cutlen;
+ md.trunc_size = min(skb->len, OVS_CB(skb)->cutlen);
md.rate_as_probability = 1;
rate = OVS_CB(skb)->probability ? OVS_CB(skb)->probability : U32_MAX;
@@ -1284,22 +1280,21 @@ static int do_execute_actions(struct datapath *dp, struct sk_buff *skb,
clone = skb_clone(skb, GFP_ATOMIC);
if (clone)
do_output(dp, clone, port, key);
- OVS_CB(skb)->cutlen = 0;
+ OVS_CB(skb)->cutlen = U32_MAX;
break;
}
case OVS_ACTION_ATTR_TRUNC: {
struct ovs_action_trunc *trunc = nla_data(a);
- if (skb->len > trunc->max_len)
- OVS_CB(skb)->cutlen = skb->len - trunc->max_len;
+ OVS_CB(skb)->cutlen = trunc->max_len;
break;
}
case OVS_ACTION_ATTR_USERSPACE:
output_userspace(dp, skb, key, a, attr,
len, OVS_CB(skb)->cutlen);
- OVS_CB(skb)->cutlen = 0;
+ OVS_CB(skb)->cutlen = U32_MAX;
if (nla_is_last(a, rem)) {
consume_skb(skb);
return 0;
@@ -1453,7 +1448,7 @@ static int do_execute_actions(struct datapath *dp, struct sk_buff *skb,
case OVS_ACTION_ATTR_PSAMPLE:
execute_psample(dp, skb, a);
- OVS_CB(skb)->cutlen = 0;
+ OVS_CB(skb)->cutlen = U32_MAX;
if (nla_is_last(a, rem)) {
consume_skb(skb);
return 0;
diff --git a/net/openvswitch/datapath.c b/net/openvswitch/datapath.c
index f0164817d9b7..eaf332b156d7 100644
--- a/net/openvswitch/datapath.c
+++ b/net/openvswitch/datapath.c
@@ -276,7 +276,7 @@ void ovs_dp_process_packet(struct sk_buff *skb, struct sw_flow_key *key)
upcall.portid = ovs_vport_find_upcall_portid(p, skb);
upcall.mru = OVS_CB(skb)->mru;
- error = ovs_dp_upcall(dp, skb, key, &upcall, 0);
+ error = ovs_dp_upcall(dp, skb, key, &upcall, U32_MAX);
switch (error) {
case 0:
case -EAGAIN:
@@ -457,7 +457,8 @@ static int queue_userspace_packet(struct datapath *dp, struct sk_buff *skb,
struct sk_buff *nskb = NULL;
struct sk_buff *user_skb = NULL; /* to be queued to userspace */
struct nlattr *nla;
- size_t len;
+ size_t msg_size;
+ size_t skb_len;
unsigned int hlen;
int err, dp_ifindex;
u64 hash;
@@ -478,7 +479,8 @@ static int queue_userspace_packet(struct datapath *dp, struct sk_buff *skb,
skb = nskb;
}
- if (nla_attr_size(skb->len) > USHRT_MAX) {
+ skb_len = min(skb->len, cutlen);
+ if (nla_attr_size(skb_len) > USHRT_MAX) {
err = -EFBIG;
goto out;
}
@@ -493,13 +495,13 @@ static int queue_userspace_packet(struct datapath *dp, struct sk_buff *skb,
* padding logic. Only perform zerocopy if padding is not required.
*/
if (dp->user_features & OVS_DP_F_UNALIGNED)
- hlen = skb_zerocopy_headlen(skb);
+ hlen = min(skb_zerocopy_headlen(skb), cutlen);
else
- hlen = skb->len;
+ hlen = skb_len;
- len = upcall_msg_size(upcall_info, hlen - cutlen,
- OVS_CB(skb)->acts_origlen);
- user_skb = genlmsg_new(len, GFP_ATOMIC);
+ msg_size = upcall_msg_size(upcall_info, hlen,
+ OVS_CB(skb)->acts_origlen);
+ user_skb = genlmsg_new(msg_size, GFP_ATOMIC);
if (!user_skb) {
err = -ENOMEM;
goto out;
@@ -560,7 +562,7 @@ static int queue_userspace_packet(struct datapath *dp, struct sk_buff *skb,
}
/* Add OVS_PACKET_ATTR_LEN when packet is truncated */
- if (cutlen > 0 &&
+ if (skb_len < skb->len &&
nla_put_u32(user_skb, OVS_PACKET_ATTR_LEN, skb->len)) {
err = -ENOBUFS;
goto out;
@@ -585,9 +587,9 @@ static int queue_userspace_packet(struct datapath *dp, struct sk_buff *skb,
err = -ENOBUFS;
goto out;
}
- nla->nla_len = nla_attr_size(skb->len - cutlen);
+ nla->nla_len = nla_attr_size(skb_len);
- err = skb_zerocopy(user_skb, skb, skb->len - cutlen, hlen);
+ err = skb_zerocopy(user_skb, skb, skb_len, hlen);
if (err)
goto out;
@@ -644,6 +646,7 @@ static int ovs_packet_cmd_execute(struct sk_buff *skb, struct genl_info *info)
packet->ignore_df = 1;
}
OVS_CB(packet)->mru = mru;
+ OVS_CB(packet)->cutlen = U32_MAX;
if (a[OVS_PACKET_ATTR_HASH]) {
hash = nla_get_u64(a[OVS_PACKET_ATTR_HASH]);
diff --git a/net/openvswitch/datapath.h b/net/openvswitch/datapath.h
index db0c3e69d66c..696640e88fa7 100644
--- a/net/openvswitch/datapath.h
+++ b/net/openvswitch/datapath.h
@@ -118,7 +118,7 @@ struct datapath {
* @mru: The maximum received fragement size; 0 if the packet is not
* fragmented.
* @acts_origlen: The netlink size of the flow actions applied to this skb.
- * @cutlen: The number of bytes from the packet end to be removed.
+ * @cutlen: The number of bytes in the packet to preserve on output.
* @probability: The sampling probability that was applied to this skb; 0 means
* no sampling has occurred; U32_MAX means 100% probability.
* @upcall_pid: Netlink socket PID to use for sending this packet to userspace;
diff --git a/net/openvswitch/vport.c b/net/openvswitch/vport.c
index 56b2e2d1a749..12741485c939 100644
--- a/net/openvswitch/vport.c
+++ b/net/openvswitch/vport.c
@@ -502,7 +502,7 @@ int ovs_vport_receive(struct vport *vport, struct sk_buff *skb,
OVS_CB(skb)->input_vport = vport;
OVS_CB(skb)->mru = 0;
- OVS_CB(skb)->cutlen = 0;
+ OVS_CB(skb)->cutlen = U32_MAX;
OVS_CB(skb)->probability = 0;
OVS_CB(skb)->upcall_pid = 0;
if (unlikely(dev_net(skb->dev) != ovs_dp_get_net(vport->dp))) {
--
2.54.0
next reply other threads:[~2026-07-07 22:16 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-07 22:16 Kyle Zeng [this message]
2026-07-07 23:16 ` [PATCH net] openvswitch: fix GSO userspace truncation underflow Ilya Maximets
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