netdev - [PATCH v4 net-next 06/13] net-sysfs: use dev_addr_sem to remove races in address

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Message-ID: <20240213063245.3605305-7-edumazet@google.com>
Date: Tue, 13 Feb 2024 06:32:38 +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 v4 net-next 06/13] net-sysfs: use dev_addr_sem to remove races
 in address_show()

Using dev_base_lock is not preventing from reading garbage.

Use dev_addr_sem instead.

v4: place dev_addr_sem extern in net/core/dev.h (Jakub Kicinski)
 Link: https://lore.kernel.org/netdev/20240212175845.10f6680a@kernel.org/

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 net/core/dev.c       |  2 +-
 net/core/dev.h       |  3 +++
 net/core/net-sysfs.c | 10 +++++++---
 3 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index c08e8830ff976e74455157d3a3b8819e8424f93c..ddf2beae547726590b1f0bbad3d40c0556d815d2 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -8951,7 +8951,7 @@ int dev_set_mac_address(struct net_device *dev, struct sockaddr *sa,
 }
 EXPORT_SYMBOL(dev_set_mac_address);
 
-static DECLARE_RWSEM(dev_addr_sem);
+DECLARE_RWSEM(dev_addr_sem);
 
 int dev_set_mac_address_user(struct net_device *dev, struct sockaddr *sa,
 			     struct netlink_ext_ack *extack)
diff --git a/net/core/dev.h b/net/core/dev.h
index a43dfe3de50ee75ee0f4b290b385378ed4a6cfdc..45892267848d7a35a09aea95f04cfd9b72204d3c 100644
--- a/net/core/dev.h
+++ b/net/core/dev.h
@@ -3,6 +3,7 @@
 #define _NET_CORE_DEV_H
 
 #include <linux/types.h>
+#include <linux/rwsem.h>
 
 struct net;
 struct net_device;
@@ -46,6 +47,8 @@ extern int		weight_p;
 extern int		dev_weight_rx_bias;
 extern int		dev_weight_tx_bias;
 
+extern struct rw_semaphore dev_addr_sem;
+
 /* rtnl helpers */
 extern struct list_head net_todo_list;
 void netdev_run_todo(void);
diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index 678e4be690821c5cdb933f5e91af2247ebecb830..23ef2df549c3036a702f3be1dca1eda14ee5e76f 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -142,17 +142,21 @@ static ssize_t name_assign_type_show(struct device *dev,
 }
 static DEVICE_ATTR_RO(name_assign_type);
 
-/* use same locking rules as GIFHWADDR ioctl's */
+/* use same locking rules as GIFHWADDR ioctl's (dev_get_mac_address()) */
 static ssize_t address_show(struct device *dev, struct device_attribute *attr,
 			    char *buf)
 {
 	struct net_device *ndev = to_net_dev(dev);
 	ssize_t ret = -EINVAL;
 
-	read_lock(&dev_base_lock);
+	down_read(&dev_addr_sem);
+
+	rcu_read_lock();
 	if (dev_isalive(ndev))
 		ret = sysfs_format_mac(buf, ndev->dev_addr, ndev->addr_len);
-	read_unlock(&dev_base_lock);
+	rcu_read_unlock();
+
+	up_read(&dev_addr_sem);
 	return ret;
 }
 static DEVICE_ATTR_RO(address);
-- 
2.43.0.687.g38aa6559b0-goog