linux-kernel - [PATCH AUTOSEL 3.18 09/12] xen/netfront: tolerate frags with no data

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Message-Id: <20181226225741.151608-9-sashal@kernel.org>
Date:   Wed, 26 Dec 2018 17:57:37 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     stable@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Juergen Gross <jgross@...e.com>,
        "David S . Miller" <davem@...emloft.net>,
        Sasha Levin <sashal@...nel.org>, netdev@...r.kernel.org
Subject: [PATCH AUTOSEL 3.18 09/12] xen/netfront: tolerate frags with no data

From: Juergen Gross <jgross@...e.com>

[ Upstream commit d81c5054a5d1d4999c7cdead7636b6cd4af83d36 ]

At least old Xen net backends seem to send frags with no real data
sometimes. In case such a fragment happens to occur with the frag limit
already reached the frontend will BUG currently even if this situation
is easily recoverable.

Modify the BUG_ON() condition accordingly.

Tested-by: Dietmar Hahn <dietmar.hahn@...fujitsu.com>
Signed-off-by: Juergen Gross <jgross@...e.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/net/xen-netfront.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index 3bbfb09af65f..5d11e60d4995 100644
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -913,7 +913,7 @@ static RING_IDX xennet_fill_frags(struct netfront_queue *queue,
 		if (skb_shinfo(skb)->nr_frags == MAX_SKB_FRAGS) {
 			unsigned int pull_to = NETFRONT_SKB_CB(skb)->pull_to;
 
-			BUG_ON(pull_to <= skb_headlen(skb));
+			BUG_ON(pull_to < skb_headlen(skb));
 			__pskb_pull_tail(skb, pull_to - skb_headlen(skb));
 		}
 		BUG_ON(skb_shinfo(skb)->nr_frags >= MAX_SKB_FRAGS);
-- 
2.19.1