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Patch "netlink: fix netlink_ack() extack race" has been added to the 4.13-stable tree

PATCH [email protected] 1 participant 1 message Nov 15, 2017

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This is a note to let you know that I've just added the patch titled

netlink: fix netlink_ack() extack race

to the 4.13-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
netlink-fix-netlink_ack-extack-race.patch
and it can be found in the queue-4.13 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

Quoted 1 line

From foo@baz Wed Nov 15 17:25:34 CET 2017

From: Johannes Berg <[email protected]>
Date: Mon, 16 Oct 2017 17:09:53 +0200
Subject: netlink: fix netlink_ack() extack race

From: Johannes Berg <[email protected]>

[ Upstream commit 48044eb490be71c203e14dd89e8bae87209eab52 ]

It seems that it's possible to toggle NETLINK_F_EXT_ACK through setsockopt() while another thread/CPU is building a message inside netlink_ack(), which could then trigger the WARN_ON()s I added since if it goes from being turned off to being turned on between allocating and filling the message, the skb could end up being too small.

Avoid this whole situation by storing the value of this flag in a separate variable and using that throughout the function instead.

Fixes 2d4bc93368f5 ("netlink: extended ACK reporting")
Signed-off-by Johannes Berg <[email protected]>
Signed-off-by David S. Miller <[email protected]>
Signed-off-by Greg Kroah-Hartman <[email protected]>
---
 net/netlink/af_netlink.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)
net/netlink/af_netlink.c +4 -4
@@ -2299,6 +2299,7 @@ void netlink_ack(struct sk_buff *in_skb,
 	size_t tlvlen = 0;
 	struct netlink_sock *nlk = nlk_sk(NETLINK_CB(in_skb).sk);
 	unsigned int flags = 0;
+	bool nlk_has_extack = nlk->flags & NETLINK_F_EXT_ACK;
 
 	/* Error messages get the original request appened, unless the user
 	 * requests to cap the error message, and get extra error data if

@@ -2309,7 +2310,7 @@ void netlink_ack(struct sk_buff *in_skb,
 			payload += nlmsg_len(nlh);
 		else
 			flags |= NLM_F_CAPPED;
-		if (nlk->flags & NETLINK_F_EXT_ACK && extack) {
+		if (nlk_has_extack && extack) {
 			if (extack->_msg)
 				tlvlen += nla_total_size(strlen(extack->_msg) + 1);
 			if (extack->bad_attr)

@@ -2318,8 +2319,7 @@ void netlink_ack(struct sk_buff *in_skb,
 	} else {
 		flags |= NLM_F_CAPPED;
 
-		if (nlk->flags & NETLINK_F_EXT_ACK &&
-		    extack && extack->cookie_len)
+		if (nlk_has_extack && extack && extack->cookie_len)
 			tlvlen += nla_total_size(extack->cookie_len);
 	}
 

@@ -2347,7 +2347,7 @@ void netlink_ack(struct sk_buff *in_skb,
 	errmsg->error = err;
 	memcpy(&errmsg->msg, nlh, payload > sizeof(*errmsg) ? nlh->nlmsg_len : sizeof(*nlh));
 
-	if (nlk->flags & NETLINK_F_EXT_ACK && extack) {
+	if (nlk_has_extack && extack) {
 		if (err) {
 			if (extack->_msg)
 				WARN_ON(nla_put_string(skb, NLMSGERR_ATTR_MSG,

Patches currently in stable-queue which might be from [email protected] are

queue-4.13/netlink-fix-netlink_ack-extack-race.patch