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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Antoine Tenart <atenart@kernel.org>,
        Alexander Duyck <alexanderduyck@fb.com>,
        Jakub Kicinski <kuba@kernel.org>
Subject: [PATCH 5.4 27/92] net-sysfs: take the rtnl lock when accessing xps_cpus_map and num_tc
Date:   Mon, 11 Jan 2021 14:01:31 +0100
Message-Id: <20210111130040.457884922@linuxfoundation.org>
In-Reply-To: <20210111130039.165470698@linuxfoundation.org>
References: <20210111130039.165470698@linuxfoundation.org>
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From: Antoine Tenart <atenart@kernel.org>

[ Upstream commit fb25038586d0064123e393cadf1fadd70a9df97a ]

Accesses to dev->xps_cpus_map (when using dev->num_tc) should be
protected by the rtnl lock, like we do for netif_set_xps_queue. I didn't
see an actual bug being triggered, but let's be safe here and take the
rtnl lock while accessing the map in sysfs.

Fixes: 184c449f91fe ("net: Add support for XPS with QoS via traffic classes")
Signed-off-by: Antoine Tenart <atenart@kernel.org>
Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/core/net-sysfs.c |   29 ++++++++++++++++++++++-------
 1 file changed, 22 insertions(+), 7 deletions(-)

--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -1235,8 +1235,8 @@ static const struct attribute_group dql_
 static ssize_t xps_cpus_show(struct netdev_queue *queue,
 			     char *buf)
 {
+	int cpu, len, ret, num_tc = 1, tc = 0;
 	struct net_device *dev = queue->dev;
-	int cpu, len, num_tc = 1, tc = 0;
 	struct xps_dev_maps *dev_maps;
 	cpumask_var_t mask;
 	unsigned long index;
@@ -1246,22 +1246,31 @@ static ssize_t xps_cpus_show(struct netd
 
 	index = get_netdev_queue_index(queue);
 
+	if (!rtnl_trylock())
+		return restart_syscall();
+
 	if (dev->num_tc) {
 		/* Do not allow XPS on subordinate device directly */
 		num_tc = dev->num_tc;
-		if (num_tc < 0)
-			return -EINVAL;
+		if (num_tc < 0) {
+			ret = -EINVAL;
+			goto err_rtnl_unlock;
+		}
 
 		/* If queue belongs to subordinate dev use its map */
 		dev = netdev_get_tx_queue(dev, index)->sb_dev ? : dev;
 
 		tc = netdev_txq_to_tc(dev, index);
-		if (tc < 0)
-			return -EINVAL;
+		if (tc < 0) {
+			ret = -EINVAL;
+			goto err_rtnl_unlock;
+		}
 	}
 
-	if (!zalloc_cpumask_var(&mask, GFP_KERNEL))
-		return -ENOMEM;
+	if (!zalloc_cpumask_var(&mask, GFP_KERNEL)) {
+		ret = -ENOMEM;
+		goto err_rtnl_unlock;
+	}
 
 	rcu_read_lock();
 	dev_maps = rcu_dereference(dev->xps_cpus_map);
@@ -1284,9 +1293,15 @@ static ssize_t xps_cpus_show(struct netd
 	}
 	rcu_read_unlock();
 
+	rtnl_unlock();
+
 	len = snprintf(buf, PAGE_SIZE, "%*pb\n", cpumask_pr_args(mask));
 	free_cpumask_var(mask);
 	return len < PAGE_SIZE ? len : -EINVAL;
+
+err_rtnl_unlock:
+	rtnl_unlock();
+	return ret;
 }
 
 static ssize_t xps_cpus_store(struct netdev_queue *queue,