tun: fix recovery from gup errors

get user pages might fail partially in tun 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>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 2 deletions

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index bfa9bb48e42d..9c61f8734a40 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1010,8 +1010,10 @@ 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;