netdev - [PATCH net] net: thunderx: don't allow jumbo frames with XDP

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Message-Id: <20190402231136.15156-1-mcroce@redhat.com>
Date:   Wed,  3 Apr 2019 01:11:36 +0200
From:   Matteo Croce <mcroce@...hat.com>
To:     netdev@...r.kernel.org
Cc:     Sunil Goutham <sgoutham@...ium.com>,
        Robert Richter <rric@...nel.org>,
        linux-arm-kernel@...ts.infradead.org
Subject: [PATCH net] net: thunderx: don't allow jumbo frames with XDP

The thunderx driver forbids to load an eBPF program if the MTU is higher
than 1500 bytes, but this can be circumvented by first loading the eBPF,
and then raising the MTU.

XDP assumes that SKBs are linear and fit in a single page, this can lead
to undefined behaviours.
Fix this by limiting the MTU to 1500 bytes if an eBPF program is loaded.

Fixes: 05c773f52b96e ("net: thunderx: Add basic XDP support")
Signed-off-by: Matteo Croce <mcroce@...hat.com>
---
 drivers/net/ethernet/cavium/thunder/nicvf_main.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/net/ethernet/cavium/thunder/nicvf_main.c b/drivers/net/ethernet/cavium/thunder/nicvf_main.c
index aa2be4807191..fe1d7513f01d 100644
--- a/drivers/net/ethernet/cavium/thunder/nicvf_main.c
+++ b/drivers/net/ethernet/cavium/thunder/nicvf_main.c
@@ -1578,6 +1578,13 @@ static int nicvf_change_mtu(struct net_device *netdev, int new_mtu)
 	struct nicvf *nic = netdev_priv(netdev);
 	int orig_mtu = netdev->mtu;
 
+	/* For now just support only the usual MTU sized frames */
+	if (nic->xdp_prog && new_mtu > 1500) {
+		netdev_warn(netdev, "Jumbo frames not yet supported with XDP, current MTU %d.\n",
+			    netdev->mtu);
+		return -EOPNOTSUPP;
+	}
+
 	netdev->mtu = new_mtu;
 
 	if (!netif_running(netdev))
-- 
2.20.1