macvtap: fix recovery from gup errors

[ 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@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
index 26106c02712051232cdcbbe5ec6fd52f03b23ca9..d91858ef98f070b2852939432e18eca8c7c042e4 100644 (file)
--- 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;