[PATCH] 8139cp: reject invalid MTU values

[PATCH] 8139cp: reject invalid MTU values

[Paolo Bonzini]

The 8139cp driver has a change_mtu function that has not been
enabled since the dawn of the git repository.  However, the
generic eth_change_mtu is not used in its place, so that
invalid MTU values can be set on the interface.

This patch salvages the broken code for the single case of
setting the MTU while the interface is down, which is safe
and also includes the range check.
---
 drivers/net/ethernet/realtek/8139cp.c |   21 +--------------------
 1 files changed, 1 insertions(+), 20 deletions(-)

diff --git a/drivers/net/ethernet/realtek/8139cp.c b/drivers/net/ethernet/realtek/8139cp.c
index cc6b391..c140b8c 100644
--- a/drivers/net/ethernet/realtek/8139cp.c
+++ b/drivers/net/ethernet/realtek/8139cp.c
@@ -1188,12 +1188,9 @@ static void cp_tx_timeout(struct net_device *dev)
 	spin_unlock_irqrestore(&cp->lock, flags);
 }
 
-#ifdef BROKEN
 static int cp_change_mtu(struct net_device *dev, int new_mtu)
 {
 	struct cp_private *cp = netdev_priv(dev);
-	int rc;
-	unsigned long flags;
 
 	/* check for invalid MTU, according to hardware limits */
 	if (new_mtu < CP_MIN_MTU || new_mtu > CP_MAX_MTU)
@@ -1206,22 +1203,8 @@ static int cp_change_mtu(struct net_device *dev, int new_mtu)
 		return 0;
 	}
 
-	spin_lock_irqsave(&cp->lock, flags);
-
-	cp_stop_hw(cp);			/* stop h/w and free rings */
-	cp_clean_rings(cp);
-
-	dev->mtu = new_mtu;
-	cp_set_rxbufsize(cp);		/* set new rx buf size */
-
-	rc = cp_init_rings(cp);		/* realloc and restart h/w */
-	cp_start_hw(cp);
-
-	spin_unlock_irqrestore(&cp->lock, flags);
-
-	return rc;
+	return -EBUSY;
 }
-#endif /* BROKEN */
 
 static const char mii_2_8139_map[8] = {
 	BasicModeCtrl,
@@ -1797,9 +1780,7 @@ static const struct net_device_ops cp_netdev_ops = {
 	.ndo_start_xmit		= cp_start_xmit,
 	.ndo_tx_timeout		= cp_tx_timeout,
 	.ndo_set_features	= cp_set_features,
-#ifdef BROKEN
 	.ndo_change_mtu		= cp_change_mtu,
-#endif
 
 #ifdef CONFIG_NET_POLL_CONTROLLER
 	.ndo_poll_controller	= cp_poll_controller,
-- 
1.7.7.6

Re: [PATCH] 8139cp: reject invalid MTU values

[David Miller]

From: Paolo Bonzini <pbonzini@redhat.com>
Date: Fri, 17 Feb 2012 13:33:15 +0100

> The 8139cp driver has a change_mtu function that has not been
> enabled since the dawn of the git repository.  However, the
> generic eth_change_mtu is not used in its place, so that
> invalid MTU values can be set on the interface.
> 
> This patch salvages the broken code for the single case of
> setting the MTU while the interface is down, which is safe
> and also includes the range check.

Well, now you can't change the MTU while the device is up
which to me is a worse problem than MTU validation because
this breaks valid things that potentially worked previously.

Also you didn't bother to give your patch a proper signoff.

You're going to have to fix cp_change_mtu() so that it does the
correct HW reset sequence when the MTU changes, otherwise I am not
going to apply this patch.