linux-kernel - [PATCH 4.4 75/78] xen/netback: Reset nr

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Message-Id: <20190822171834.203954783@linuxfoundation.org>
Date:   Thu, 22 Aug 2019 10:19:19 -0700
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Ross Lagerwall <ross.lagerwall@...rix.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.4 75/78] xen/netback: Reset nr_frags before freeing skb

From: Ross Lagerwall <ross.lagerwall@...rix.com>

[ Upstream commit 3a0233ddec554b886298de2428edb5c50a20e694 ]

At this point nr_frags has been incremented but the frag does not yet
have a page assigned so freeing the skb results in a crash. Reset
nr_frags before freeing the skb to prevent this.

Signed-off-by: Ross Lagerwall <ross.lagerwall@...rix.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/net/xen-netback/netback.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -1421,6 +1421,7 @@ static void xenvif_tx_build_gops(struct
 			skb_shinfo(skb)->nr_frags = MAX_SKB_FRAGS;
 			nskb = xenvif_alloc_skb(0);
 			if (unlikely(nskb == NULL)) {
+				skb_shinfo(skb)->nr_frags = 0;
 				kfree_skb(skb);
 				xenvif_tx_err(queue, &txreq, idx);
 				if (net_ratelimit())
@@ -1436,6 +1437,7 @@ static void xenvif_tx_build_gops(struct
 
 			if (xenvif_set_skb_gso(queue->vif, skb, gso)) {
 				/* Failure in xenvif_set_skb_gso is fatal. */
+				skb_shinfo(skb)->nr_frags = 0;
 				kfree_skb(skb);
 				kfree_skb(nskb);
 				break;