netdev - [PATCH net] netlink: Use netlink header as base to calculate bad attribute offset

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Message-Id: <20200226184734.1866-1-pablo@netfilter.org>
Date:   Wed, 26 Feb 2020 19:47:34 +0100
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     netdev@...r.kernel.org
Cc:     netfilter-devel@...r.kernel.org, davem@...emloft.net,
        johannes.berg@...el.com
Subject: [PATCH net] netlink: Use netlink header as base to calculate bad attribute offset

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@...filter.org>
---
 net/netlink/af_netlink.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index edf3e285e242..5313f1cec170 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -2434,7 +2434,7 @@ void netlink_ack(struct sk_buff *in_skb, struct nlmsghdr *nlh, int err,
 							       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,
-- 
2.11.0