[PATCH v3] airo: Fix read overflows sending packets

[Dan Carpenter <dan.carpenter@oracle.com>]

The problem is that we always copy a minimum of ETH_ZLEN (60) bytes from
skb->data even when skb->len is less than ETH_ZLEN so it leads to a read
overflow.

The fix is to pad skb->data to at least ETH_ZLEN bytes.

Cc: <stable@vger.kernel.org>
Reported-by: Hu Jiahui <kirin.say@gmail.com>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
---
v2: remove an unnecessary if statement
    increment the ->tx_dropped count on failure
    fix found two more instances of the same bug.
    fix typo in the "Cc: <stable@vger.kernel.org>" tag
v3: I had thought that skb_padto() updated skb->len so that it would
    always be more than ETH_ZLEN meaning that we could delete the checks
    for smaller values:  "len = skb->len < ETH_ZLEN ? ETH_ZLEN : skb->len;"
    But I was wrong and those are still required.

 drivers/net/wireless/cisco/airo.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/net/wireless/cisco/airo.c b/drivers/net/wireless/cisco/airo.c
index 8363f91df7ea7..827bb6d74815a 100644
--- a/drivers/net/wireless/cisco/airo.c
+++ b/drivers/net/wireless/cisco/airo.c
@@ -1925,6 +1925,10 @@ static netdev_tx_t mpi_start_xmit(struct sk_buff *skb,
 		airo_print_err(dev->name, "%s: skb == NULL!",__func__);
 		return NETDEV_TX_OK;
 	}
+	if (skb_padto(skb, ETH_ZLEN)) {
+		dev->stats.tx_dropped++;
+		return NETDEV_TX_OK;
+	}
 	npacks = skb_queue_len (&ai->txq);
 
 	if (npacks >= MAXTXQ - 1) {
@@ -2127,6 +2131,10 @@ static netdev_tx_t airo_start_xmit(struct sk_buff *skb,
 		airo_print_err(dev->name, "%s: skb == NULL!", __func__);
 		return NETDEV_TX_OK;
 	}
+	if (skb_padto(skb, ETH_ZLEN)) {
+		dev->stats.tx_dropped++;
+		return NETDEV_TX_OK;
+	}
 
 	/* Find a vacant FID */
 	for( i = 0; i < MAX_FIDS / 2 && (fids[i] & 0xffff0000); i++ );
@@ -2201,6 +2209,10 @@ static netdev_tx_t airo_start_xmit11(struct sk_buff *skb,
 		airo_print_err(dev->name, "%s: skb == NULL!", __func__);
 		return NETDEV_TX_OK;
 	}
+	if (skb_padto(skb, ETH_ZLEN)) {
+		dev->stats.tx_dropped++;
+		return NETDEV_TX_OK;
+	}
 
 	/* Find a vacant FID */
 	for( i = MAX_FIDS / 2; i < MAX_FIDS && (fids[i] & 0xffff0000); i++ );
-- 
2.26.2