Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Ross Lagerwall <ross.lagerwall@citrix.com>,
        "David S. Miller" <davem@davemloft.net>
Subject: [PATCH 4.19 82/85] xen/netback: Reset nr_frags before freeing skb
Date:   Thu, 22 Aug 2019 10:19:55 -0700
Message-Id: <20190822171734.620711532@linuxfoundation.org>
In-Reply-To: <20190822171731.012687054@linuxfoundation.org>
References: <20190822171731.012687054@linuxfoundation.org>
User-Agent: quilt/0.66
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

From: Ross Lagerwall <ross.lagerwall@citrix.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@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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
@@ -925,6 +925,7 @@ 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, extra_count, idx);
 				if (net_ratelimit())
@@ -940,6 +941,7 @@ 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;