[PATCH 4.14 08/99] netlink: Use netlink header as base to calculate bad attribute offset

[Greg Kroah-Hartman]

From: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>

[ Upstream commit 84b3268027641401bb8ad4427a90a3cce2eb86f5 ]

Userspace might send a batch that is composed of several netlink
messages. The netlink_ack() function must use the pointer to the netlink
header as base to calculate the bad attribute offset.

Fixes: 2d4bc93368f5 ("netlink: extended ACK reporting")
Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 net/netlink/af_netlink.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -2389,7 +2389,7 @@ void netlink_ack(struct sk_buff *in_skb,
 							       in_skb->len))
 				WARN_ON(nla_put_u32(skb, NLMSGERR_ATTR_OFFS,
 						    (u8 *)extack->bad_attr -
-						    in_skb->data));
+						    (u8 *)nlh));
 		} else {
 			if (extack->cookie_len)
 				WARN_ON(nla_put(skb, NLMSGERR_ATTR_COOKIE,