linux-kernel - [PATCH net 1/2] rtnetlink: Fix rtnl_net_cmp

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Message-Id: <20250212-rtnetlink_leak-v1-1-27bce9a3ac9a@bootlin.com>
Date: Wed, 12 Feb 2025 09:23:47 +0100
From: "Bastien Curutchet (eBPF Foundation)" <bastien.curutchet@...tlin.com>
To: "David S. Miller" <davem@...emloft.net>, 
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
 Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
 Nikolay Aleksandrov <razor@...ckwall.org>, 
 Kuniyuki Iwashima <kuniyu@...zon.com>
Cc: Alexis Lothore <alexis.lothore@...tlin.com>, 
 Thomas Petazzoni <thomas.petazzoni@...tlin.com>, netdev@...r.kernel.org, 
 linux-kernel@...r.kernel.org, 
 "Bastien Curutchet (eBPF Foundation)" <bastien.curutchet@...tlin.com>, 
 stable@...r.kernel.org
Subject: [PATCH net 1/2] rtnetlink: Fix rtnl_net_cmp_locks() when DEBUG is
 off

rtnl_net_cmp_locks() always returns -1 if CONFIG_DEBUG_NET_SMALL_RTNL is
disabled. However, if CONFIG_DEBUG_NET_SMALL_RTNL is enabled, it returns 0
when both inputs are equal. It is then used by rtnl_nets_add() to call
put_net() if the net to be added is already present in the struct
rtnl_nets. As a result, when rtnl_nets_add() is called on an already
present net, put_net() is called only if DEBUG is on.

Add the input comparison in the DEBUG off case so that put_net() is always
called in this scenario.

Fixes: cbaaa6326bc5 ("rtnetlink: Introduce struct rtnl_nets and helpers.")
Cc: stable@...r.kernel.org
Signed-off-by: Bastien Curutchet (eBPF Foundation) <bastien.curutchet@...tlin.com>
---
 net/core/rtnetlink.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index cb7fad8d1f95ff287810229c341de6a6d20a9c07..94111d3383788566f2296039e68549e2b40d5a4a 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -275,6 +275,9 @@ EXPORT_SYMBOL(lockdep_rtnl_net_is_held);
 #else
 static int rtnl_net_cmp_locks(const struct net *net_a, const struct net *net_b)
 {
+	if (net_eq(net_a, net_b))
+		return 0;
+
 	/* No need to swap */
 	return -1;
 }

-- 
2.48.1