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netlink: extack needs to be reset each time through loop

PATCH In review David Ahern 2 participants 2 messages Jan 10, 2018 – Jan 15, 2018

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David Ahern

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#0 lore raw

PATCH 1/1 netlink: extack needs to be reset each time through loop

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 [email protected]
Signed-off-by David Ahern <[email protected]>
---
 net/netlink/af_netlink.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
net/netlink/af_netlink.c +2 -1
index 972bfe113043..ee8252d7b3d4 100644
@@ -2417,7 +2417,7 @@ int netlink_rcv_skb(struct sk_buff *skb, int (*cb)(struct sk_buff *,
 						   struct nlmsghdr *,
 						   struct netlink_ext_ack *))
 {
-	struct netlink_ext_ack extack = {};
+	struct netlink_ext_ack extack;
 	struct nlmsghdr *nlh;
 	int err;
 

@@ -2438,6 +2438,7 @@ int netlink_rcv_skb(struct sk_buff *skb, int (*cb)(struct sk_buff *,
 		if (nlh->nlmsg_type < NLMSG_MIN_TYPE)
 			goto ack;
 
+		memset(&extack, 0, sizeof(extack));
 		err = cb(skb, nlh, &extack);
 		if (err == -EINTR)
 			goto skip;
Signature · 1 line
2.11.0
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#1 lore raw

From: David Ahern <[email protected]>
Date: Wed, 10 Jan 2018 13:00:39 -0800

Quoted 8 lines

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 [email protected]
Signed-off-by David Ahern <[email protected]>

Applied and queued up for -stable, thanks David.