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

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Message-Id: <1445527642-15567-1-git-send-email-Jason@zx2c4.com>
Date:	Thu, 22 Oct 2015 17:27:22 +0200
From:	"Jason A. Donenfeld" <Jason@...c4.com>
To:	jeffrey.t.kirsher@...el.com, jesse.brandeburg@...el.com,
	shannon.nelson@...el.com, carolyn.wyborny@...el.com,
	donald.c.skidmore@...el.com, matthew.vick@...el.com,
	john.ronciak@...el.com, mitch.a.williams@...el.com,
	intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc:	"Jason A. Donenfeld" <Jason@...c4.com>
Subject: [PATCH] e1000: free skb when returning on -ENOMEM error

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@...c4.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

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