linux-kernel - [PATCH] xen/netfront: tolerate frags with no data

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Message-Id: <20181218150619.6964-1-jgross@suse.com>
Date:   Tue, 18 Dec 2018 16:06:19 +0100
From:   Juergen Gross <jgross@...e.com>
To:     linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        xen-devel@...ts.xenproject.org
Cc:     davem@...emloft.net, sstabellini@...nel.org,
        boris.ostrovsky@...cle.com, Juergen Gross <jgross@...e.com>,
        stable@...r.kernel.org
Subject: [PATCH] xen/netfront: tolerate frags with no data

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.

Cc: stable@...r.kernel.org
Tested-by: Dietmar Hahn <dietmar.hahn@...fujitsu.com>
Signed-off-by: Juergen Gross <jgross@...e.com>
---
 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 f17f602e6171..5b97cc946d70 100644
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -905,7 +905,7 @@ 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));
 		}
 		if (unlikely(skb_shinfo(skb)->nr_frags >= MAX_SKB_FRAGS)) {
-- 
2.16.4