netdev - [PATCH net-next 1/8] rtnetlink: do not depend on RTNL for IFLA

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Message-ID: <20240503192059.3884225-2-edumazet@google.com>
Date: Fri,  3 May 2024 19:20:52 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, eric.dumazet@...il.com, 
	Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net-next 1/8] rtnetlink: do not depend on RTNL for IFLA_QDISC output

dev->qdisc can be read using RCU protection.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 net/core/rtnetlink.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 283e42f48af68504af193ed5763d4e0fcd667d99..f4a87f89d5cde0cdd35c156d78ebe31511d4a31c 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -1832,7 +1832,6 @@ static int rtnl_fill_ifinfo(struct sk_buff *skb,
 	if (tgt_netnsid >= 0 && nla_put_s32(skb, IFLA_TARGET_NETNSID, tgt_netnsid))
 		goto nla_put_failure;
 
-	qdisc = rtnl_dereference(dev->qdisc);
 	if (nla_put_string(skb, IFLA_IFNAME, dev->name) ||
 	    nla_put_u32(skb, IFLA_TXQLEN, dev->tx_queue_len) ||
 	    nla_put_u8(skb, IFLA_OPERSTATE,
@@ -1857,8 +1856,6 @@ static int rtnl_fill_ifinfo(struct sk_buff *skb,
 #endif
 	    put_master_ifindex(skb, dev) ||
 	    nla_put_u8(skb, IFLA_CARRIER, netif_carrier_ok(dev)) ||
-	    (qdisc &&
-	     nla_put_string(skb, IFLA_QDISC, qdisc->ops->id)) ||
 	    nla_put_ifalias(skb, dev) ||
 	    nla_put_u32(skb, IFLA_CARRIER_CHANGES,
 			atomic_read(&dev->carrier_up_count) +
@@ -1924,6 +1921,9 @@ static int rtnl_fill_ifinfo(struct sk_buff *skb,
 		goto nla_put_failure;
 
 	rcu_read_lock();
+	qdisc = rcu_dereference(dev->qdisc);
+	if (qdisc && nla_put_string(skb, IFLA_QDISC, qdisc->ops->id))
+		goto nla_put_failure_rcu;
 	if (rtnl_fill_link_af(skb, dev, ext_filter_mask))
 		goto nla_put_failure_rcu;
 	if (rtnl_fill_link_ifmap(skb, dev))
-- 
2.45.0.rc1.225.g2a3ae87e7f-goog