[PATCH 6.1 290/609] openvswitch: fix GSO userspace truncation underflow

6.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Kyle Zeng <[email protected]>

[ Upstream commit 4032f8ed10fcb84d41c508dfb04be96589f78dfe ]

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: [email protected]
Assisted-by: Codex:gpt-5.5
Signed-off-by: Kyle Zeng <[email protected]>
Reviewed-by: Ilya Maximets <[email protected]>
Reviewed-by: Aaron Conole <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Paolo Abeni <[email protected]>
[6.1.y supports neither OVS_ACTION_ATTR_PSAMPLE nor OVS drop reasons]
Signed-off-by: Ilya Maximets <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>
---
 net/openvswitch/actions.c  | 15 +++++----------
 net/openvswitch/datapath.c | 25 ++++++++++++++-----------
 net/openvswitch/datapath.h |  2 +-
 net/openvswitch/vport.c    |  2 +-
 4 files changed, 21 insertions(+), 23 deletions(-)

diff --git a/net/openvswitch/actions.c b/net/openvswitch/actions.c
index f7cc87e67d3c8c..18e419affb5727 100644
--- a/net/openvswitch/actions.c
+++ b/net/openvswitch/actions.c
@@ -856,12 +856,8 @@ 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))) {
@@ -1242,22 +1238,21 @@ 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;
 			break;
 
 		case OVS_ACTION_ATTR_HASH:
diff --git a/net/openvswitch/datapath.c b/net/openvswitch/datapath.c
index 0c0d89470145a1..1181807f2b5020 100644
--- a/net/openvswitch/datapath.c
+++ b/net/openvswitch/datapath.c
@@ -251,7 +251,7 @@ 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:
@@ -414,7 +414,8 @@ 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;
@@ -435,7 +436,8 @@ 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;
 	}
@@ -450,13 +452,13 @@ 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;
@@ -517,7 +519,7 @@ 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;
@@ -542,9 +544,9 @@ 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;
 
@@ -601,6 +603,7 @@ 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 0cd29971a907ca..88156a677f22c5 100644
--- a/net/openvswitch/datapath.h
+++ b/net/openvswitch/datapath.h
@@ -114,7 +114,7 @@ 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.
  */
 struct ovs_skb_cb {
 	struct vport		*input_vport;
diff --git a/net/openvswitch/vport.c b/net/openvswitch/vport.c
index 5d7af559a20bed..e83aa6417ffde0 100644
--- a/net/openvswitch/vport.c
+++ b/net/openvswitch/vport.c
@@ -438,7 +438,7 @@ 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;
 	if (unlikely(dev_net(skb->dev) != ovs_dp_get_net(vport->dp))) {
 		u32 mark;
 
-- 
2.53.0