linux-kernel - [03/84] macvtap: fix recovery from gup errors

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Message-ID: <lsq.1375276989.608960498@decadent.org.uk>
Date:	Wed, 31 Jul 2013 15:23:09 +0200
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "Jason Wang" <jasowang@...hat.com>,
	"Brad Hubbard" <bhubbard@...hat.com>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: [03/84] macvtap: fix recovery from gup errors

3.2.50-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: "Michael S. Tsirkin" <mst@...hat.com>

[ Upstream commit 4c7ab054ab4f5d63625508ed6f8a607184cae7c2 ]

get user pages might fail partially in macvtap zero copy
mode. To recover we need to put all pages that we got,
but code used a wrong index resulting in double-free
errors.

Reported-by: Brad Hubbard <bhubbard@...hat.com>
Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
Acked-by: Jason Wang <jasowang@...hat.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/net/macvtap.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
index 26106c0..d91858e 100644
--- a/drivers/net/macvtap.c
+++ b/drivers/net/macvtap.c
@@ -532,8 +532,10 @@ static int zerocopy_sg_from_iovec(struct sk_buff *skb, const struct iovec *from,
 			return -EMSGSIZE;
 		num_pages = get_user_pages_fast(base, size, 0, &page[i]);
 		if (num_pages != size) {
-			for (i = 0; i < num_pages; i++)
-				put_page(page[i]);
+			int j;
+
+			for (j = 0; j < num_pages; j++)
+				put_page(page[i + j]);
 			return -EFAULT;
 		}
 		truesize = size * PAGE_SIZE;

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