netdev - [PATCH 3/6] xen-netfront: do not use data already exposed to backend

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Date:   Mon, 30 Apr 2018 23:01:47 +0200
From:   Marek Marczykowski-Górecki 
        <marmarek@...isiblethingslab.com>
To:     xen-devel@...ts.xenproject.org
Cc:     Marek Marczykowski-Górecki 
        <marmarek@...isiblethingslab.com>, stable@...r.kernel.org,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        netdev@...r.kernel.org (open list:NETWORKING DRIVERS),
        linux-kernel@...r.kernel.org (open list)
Subject: [PATCH 3/6] xen-netfront: do not use data already exposed to backend

Backend may freely modify anything on shared page, so use data which was
supposed to be written there, instead of reading it back from the shared
page.

This is complementary to XSA155.

CC: stable@...r.kernel.org
Signed-off-by: Marek Marczykowski-Górecki <marmarek@...isiblethingslab.com>
---
 drivers/net/xen-netfront.c |  9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index dc99763..934b8a4 100644
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -458,7 +458,7 @@ static void xennet_tx_setup_grant(unsigned long gfn, unsigned int offset,
 	tx->flags = 0;
 
 	info->tx = tx;
-	info->size += tx->size;
+	info->size += len;
 }
 
 static struct xen_netif_tx_request *xennet_make_first_txreq(
@@ -574,7 +574,7 @@ static int xennet_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	int slots;
 	struct page *page;
 	unsigned int offset;
-	unsigned int len;
+	unsigned int len, this_len;
 	unsigned long flags;
 	struct netfront_queue *queue = NULL;
 	unsigned int num_queues = dev->real_num_tx_queues;
@@ -634,14 +634,15 @@ static int xennet_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	}
 
 	/* First request for the linear area. */
+	this_len = min_t(unsigned int, XEN_PAGE_SIZE - offset, len);
 	first_tx = tx = xennet_make_first_txreq(queue, skb,
 						page, offset, len);
-	offset += tx->size;
+	offset += this_len;
 	if (offset == PAGE_SIZE) {
 		page++;
 		offset = 0;
 	}
-	len -= tx->size;
+	len -= this_len;
 
 	if (skb->ip_summed == CHECKSUM_PARTIAL)
 		/* local packet? */
-- 
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