Re: [Intel-wired-lan] [PATCH] e1000: free skb when returning on -ENOMEM error

From: Alexander Duyck
Date: Thu Oct 22 2015 - 11:59:36 EST


On 10/22/2015 08:27 AM, Jason A. Donenfeld wrote:
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@xxxxxxxxx>
---
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


This patch makes no sense. The function eth_skb_pad will have freed the skb if it is returning an error value. As such there is nothing to free. The code was correct before.

- Alex
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/