[ 017/171 ] vhost/net: fix heads usage of ubuf_info

From: Steven Rostedt
Date: Thu Apr 11 2013 - 16:37:27 EST stable review patch.
If anyone has any objections, please let me know.


From: "Michael S. Tsirkin" <mst@xxxxxxxxxx>

[ Upstream commit 46aa92d1ba162b4b3d6b7102440e459d4e4ee255 ]

ubuf info allocator uses guest controlled head as an index,
so a malicious guest could put the same head entry in the ring twice,
and we will get two callbacks on the same value.
To fix use upend_idx which is guaranteed to be unique.

Reported-by: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
Cc: stable@xxxxxxxxxx
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
drivers/vhost/net.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 7f93f34..156a360 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -235,7 +235,8 @@ static void handle_tx(struct vhost_net *net)
msg.msg_controllen = 0;
ubufs = NULL;
} else {
- struct ubuf_info *ubuf = &vq->ubuf_info[head];
+ struct ubuf_info *ubuf;
+ ubuf = vq->ubuf_info + vq->upend_idx;

vq->heads[vq->upend_idx].len = len;
ubuf->callback = vhost_zerocopy_callback;

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