linux-kernel - [PATCH 4.4 190/312] ipv4: do not abuse GFP_ATOMIC in inet_netconf_notify

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Message-Id: <20200508123137.827396603@linuxfoundation.org>
Date:   Fri,  8 May 2020 14:33:01 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
        Nicolas Dichtel <nicolas.dichtel@...nd.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.4 190/312] ipv4: do not abuse GFP_ATOMIC in inet_netconf_notify_devconf()

From: Eric Dumazet <edumazet@...gle.com>

commit fa17806cde76fb1087532f07e72aa757a30e0500 upstream.

inet_forward_change() runs with RTNL held.
We are allowed to sleep if required.

If we use __in_dev_get_rtnl() instead of __in_dev_get_rcu(),
we no longer have to use GFP_ATOMIC allocations in
inet_netconf_notify_devconf(), meaning we are less likely to miss
notifications under memory pressure, and wont touch precious memory
reserves either and risk dropping incoming packets.

inet_netconf_get_devconf() can also use GFP_KERNEL allocation.

Fixes: edc9e748934c ("rtnl/ipv4: use netconf msg to advertise forwarding status")
Fixes: 9e5511106f99 ("rtnl/ipv4: add support of RTM_GETNETCONF")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Nicolas Dichtel <nicolas.dichtel@...nd.com>
Acked-by: Nicolas Dichtel <nicolas.dichtel@...nd.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 net/ipv4/devinet.c |   12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

--- a/net/ipv4/devinet.c
+++ b/net/ipv4/devinet.c
@@ -1814,7 +1814,7 @@ void inet_netconf_notify_devconf(struct
 	struct sk_buff *skb;
 	int err = -ENOBUFS;
 
-	skb = nlmsg_new(inet_netconf_msgsize_devconf(type), GFP_ATOMIC);
+	skb = nlmsg_new(inet_netconf_msgsize_devconf(type), GFP_KERNEL);
 	if (!skb)
 		goto errout;
 
@@ -1826,7 +1826,7 @@ void inet_netconf_notify_devconf(struct
 		kfree_skb(skb);
 		goto errout;
 	}
-	rtnl_notify(skb, net, 0, RTNLGRP_IPV4_NETCONF, NULL, GFP_ATOMIC);
+	rtnl_notify(skb, net, 0, RTNLGRP_IPV4_NETCONF, NULL, GFP_KERNEL);
 	return;
 errout:
 	if (err < 0)
@@ -1883,7 +1883,7 @@ static int inet_netconf_get_devconf(stru
 	}
 
 	err = -ENOBUFS;
-	skb = nlmsg_new(inet_netconf_msgsize_devconf(-1), GFP_ATOMIC);
+	skb = nlmsg_new(inet_netconf_msgsize_devconf(-1), GFP_KERNEL);
 	if (!skb)
 		goto errout;
 
@@ -2007,16 +2007,16 @@ static void inet_forward_change(struct n
 
 	for_each_netdev(net, dev) {
 		struct in_device *in_dev;
+
 		if (on)
 			dev_disable_lro(dev);
-		rcu_read_lock();
-		in_dev = __in_dev_get_rcu(dev);
+
+		in_dev = __in_dev_get_rtnl(dev);
 		if (in_dev) {
 			IN_DEV_CONF_SET(in_dev, FORWARDING, on);
 			inet_netconf_notify_devconf(net, NETCONFA_FORWARDING,
 						    dev->ifindex, &in_dev->cnf);
 		}
-		rcu_read_unlock();
 	}
 }