net: don't allow user space to lift the device limits

Up until commit 46e6b992c250 ("rtnetlink: allow GSO maximums to
be set on device creation") the gso_max_segs and gso_max_size
of a device were not controlled from user space.

The quoted commit added the ability to control them because of
the following setup:

 netns A  |  netns B
     veth<->veth   eth0

If eth0 has TSO limitations and user wants to efficiently forward
traffic between eth0 and the veths they should copy the TSO
limitations of eth0 onto the veths. This would happen automatically
for macvlans or ipvlan but veth users are not so lucky (given the
loose coupling).

Unfortunately the commit in question allowed users to also override
the limits on real HW devices.

It may be useful to control the max GSO size and someone may be using
that ability (not that I know of any user), so create a separate set
of knobs to reliably record the TSO limitations. Validate the user
requests.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 35 insertions, 0 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index eef1d19b130f..6ae085b11373 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2993,6 +2993,39 @@ undo_rx:
 EXPORT_SYMBOL(netif_set_real_num_queues);
 
 /**
+ * netif_set_tso_max_size() - set the max size of TSO frames supported
+ * @dev:	netdev to update
+ * @size:	max skb->len of a TSO frame
+ *
+ * Set the limit on the size of TSO super-frames the device can handle.
+ * Unless explicitly set the stack will assume the value of %GSO_MAX_SIZE.
+ */
+void netif_set_tso_max_size(struct net_device *dev, unsigned int size)
+{
+	dev->tso_max_size = size;
+	if (size < READ_ONCE(dev->gso_max_size))
+		netif_set_gso_max_size(dev, size);
+}
+EXPORT_SYMBOL(netif_set_tso_max_size);
+
+/**
+ * netif_set_tso_max_segs() - set the max number of segs supported for TSO
+ * @dev:	netdev to update
+ * @segs:	max number of TCP segments
+ *
+ * Set the limit on the number of TCP segments the device can generate from
+ * a single TSO super-frame.
+ * Unless explicitly set the stack will assume the value of %GSO_MAX_SEGS.
+ */
+void netif_set_tso_max_segs(struct net_device *dev, unsigned int segs)
+{
+	dev->tso_max_segs = segs;
+	if (segs < READ_ONCE(dev->gso_max_segs))
+		netif_set_gso_max_segs(dev, segs);
+}
+EXPORT_SYMBOL(netif_set_tso_max_segs);
+
+/**
  * netif_inherit_tso_max() - copy all TSO limits from a lower device to an upper
  * @to:		netdev to update
  * @from:	netdev from which to copy the limits
@@ -10572,6 +10605,8 @@ struct net_device *alloc_netdev_mqs(int sizeof_priv, const char *name,
 	dev->gso_max_size = GSO_MAX_SIZE;
 	dev->gso_max_segs = GSO_MAX_SEGS;
 	dev->gro_max_size = GRO_MAX_SIZE;
+	dev->tso_max_size = TSO_LEGACY_MAX_SIZE;
+	dev->tso_max_segs = TSO_MAX_SEGS;
 	dev->upper_level = 1;
 	dev->lower_level = 1;
 #ifdef CONFIG_LOCKDEP