[PATCH] e1000: free skb when returning on -ENOMEM error

["Jason A. Donenfeld" <Jason@zx2c4.com>]

eth_skb_pad returns 0 if it was successful, or -ENOMEM if it was not. In
that case, this function exits early. Some early exits return with
NETDEV_TX_BUSY, which queues the skb up to be tried again, and so the
skb should not be freed. Other early exits return with NETDEV_TX_OK,
like this one, in which case it's imperative that the skb is freed,
since it is not queued back up. In this case, upon receiving -ENOMEM
from eth_skb_pad, the function exits early with NETDEV_TX_OK, but
forgets to free the skb. This patch fixes that.

In a low memory situation, in which the GFP_ATOMIC allocation from
eth_skb_pad fails, if a network device is transmitting repeatedly, this
bug could lead to rapidly leaking memory that could only be recovered by
a reboot or crash.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 drivers/net/ethernet/intel/e1000/e1000_main.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/intel/e1000/e1000_main.c b/drivers/net/ethernet/intel/e1000/e1000_main.c
index 74dc150..0d6b4c8 100644
--- a/drivers/net/ethernet/intel/e1000/e1000_main.c
+++ b/drivers/net/ethernet/intel/e1000/e1000_main.c
@@ -3130,8 +3130,10 @@ static netdev_tx_t e1000_xmit_frame(struct sk_buff *skb,
 	 * packets may get corrupted during padding by HW.
 	 * To WA this issue, pad all small packets manually.
 	 */
-	if (eth_skb_pad(skb))
+	if (eth_skb_pad(skb)) {
+		dev_kfree_skb_any(skb);
 		return NETDEV_TX_OK;
+	}
 
 	mss = skb_shinfo(skb)->gso_size;
 	/* The controller does a simple calculation to
-- 
2.6.2