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

[<gregkh@linuxfoundation.org>]

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 <stable@vger.kernel.org> know about it.


>From foo@baz Wed Nov 15 17:25:34 CET 2017
From: Johannes Berg <johannes.berg@intel.com>
Date: Mon, 16 Oct 2017 17:09:53 +0200
Subject: netlink: fix netlink_ack() extack race

From: Johannes Berg <johannes.berg@intel.com>


[ 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 <johannes.berg@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/netlink/af_netlink.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -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 johannes.berg@intel.com are

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