[PATCH net-next] sfc: check MTU against minimum threshold

[Bert Kenward]

Reported-by: Ma Yuying <y...@redhat.com>
Suggested-by: Jarod Wilson <ja...@redhat.com>
Signed-off-by: Bert Kenward <bkenw...@solarflare.com>
---
 drivers/net/ethernet/sfc/efx.c        | 12 +++++++++++-
 drivers/net/ethernet/sfc/net_driver.h |  3 +++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/sfc/efx.c b/drivers/net/ethernet/sfc/efx.c
index f3826ae..3cf3557 100644
--- a/drivers/net/ethernet/sfc/efx.c
+++ b/drivers/net/ethernet/sfc/efx.c
@@ -2263,8 +2263,18 @@ static int efx_change_mtu(struct net_device *net_dev, 
int new_mtu)
        rc = efx_check_disabled(efx);
        if (rc)
                return rc;
-       if (new_mtu > EFX_MAX_MTU)
+       if (new_mtu > EFX_MAX_MTU) {
+               netif_err(efx, drv, efx->net_dev,
+                         "Requested MTU of %d too big (max: %d)\n",
+                         new_mtu, EFX_MAX_MTU);
                return -EINVAL;
+       }
+       if (new_mtu < EFX_MIN_MTU) {
+               netif_err(efx, drv, efx->net_dev,
+                         "Requested MTU of %d too small (min: %d)\n",
+                         new_mtu, EFX_MIN_MTU);
+               return -EINVAL;
+       }
 
        netif_dbg(efx, drv, efx->net_dev, "changing MTU to %d\n", new_mtu);
 
diff --git a/drivers/net/ethernet/sfc/net_driver.h 
b/drivers/net/ethernet/sfc/net_driver.h
index 0a2504b..99d8c82 100644
--- a/drivers/net/ethernet/sfc/net_driver.h
+++ b/drivers/net/ethernet/sfc/net_driver.h
@@ -76,6 +76,9 @@
 /* Maximum possible MTU the driver supports */
 #define EFX_MAX_MTU (9 * 1024)
 
+/* Minimum MTU, from RFC791 (IP) */
+#define EFX_MIN_MTU 68
+
 /* Size of an RX scatter buffer.  Small enough to pack 2 into a 4K page,
  * and should be a multiple of the cache line size.
  */
-- 
2.7.4