[PATCH net] tun: fix recovery from gup errors

From: Michael S. Tsirkin
Date: Sun Jun 23 2013 - 10:18:35 EST

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

Reported-by: Brad Hubbard <bhubbard@xxxxxxxxxx>
Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>

I haven't figured out why do we get failures,
but recovery is clearly wrong.

This is also -stable material.

drivers/net/tun.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index bfa9bb4..c098b1e 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1010,8 +1010,9 @@ 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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