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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        syzbot+315fa6766d0f7c359327@syzkaller.appspotmail.com,
        David Ahern <dsahern@gmail.com>,
        "David S. Miller" <davem@davemloft.net>
Subject: [PATCH 4.14 50/71] netlink: extack needs to be reset each time through loop
Date:   Mon, 29 Jan 2018 13:57:18 +0100
Message-Id: <20180129123830.768371527@linuxfoundation.org>
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4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: David Ahern <dsahern@gmail.com>


[ Upstream commit cbbdf8433a5f117b1a2119ea30fc651b61ef7570 ]

syzbot triggered the WARN_ON in netlink_ack testing the bad_attr value.
The problem is that netlink_rcv_skb loops over the skb repeatedly invoking
the callback and without resetting the extack leaving potentially stale
data. Initializing each time through avoids the WARN_ON.

Fixes: 2d4bc93368f5a ("netlink: extended ACK reporting")
Reported-by: syzbot+315fa6766d0f7c359327@syzkaller.appspotmail.com
Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/netlink/af_netlink.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -2393,7 +2393,7 @@ int netlink_rcv_skb(struct sk_buff *skb,
 						   struct nlmsghdr *,
 						   struct netlink_ext_ack *))
 {
-	struct netlink_ext_ack extack = {};
+	struct netlink_ext_ack extack;
 	struct nlmsghdr *nlh;
 	int err;
 
@@ -2414,6 +2414,7 @@ int netlink_rcv_skb(struct sk_buff *skb,
 		if (nlh->nlmsg_type < NLMSG_MIN_TYPE)
 			goto ack;
 
+		memset(&extack, 0, sizeof(extack));
 		err = cb(skb, nlh, &extack);
 		if (err == -EINTR)
 			goto skip;