[PATCH net] net: Fix data race around dev->flags in netif_is_bond_master

[Jeongjun Park]

BUG: KCSAN: data-race in __dev_change_flags / is_upper_ndev_bond_master_filter

read-write to 0xffff888112d970b0 of 4 bytes by task 4888 on cpu 0:
 __dev_change_flags+0x9a/0x410 net/core/dev.c:8755
 rtnl_configure_link net/core/rtnetlink.c:3321 [inline]
 rtnl_newlink_create net/core/rtnetlink.c:3518 [inline]
 __rtnl_newlink net/core/rtnetlink.c:3730 [inline]
 rtnl_newlink+0x121e/0x1690 net/core/rtnetlink.c:3743
 rtnetlink_rcv_msg+0x85e/0x910 net/core/rtnetlink.c:6635
 netlink_rcv_skb+0x12c/0x230 net/netlink/af_netlink.c:2564
 rtnetlink_rcv+0x1c/0x30 net/core/rtnetlink.c:6653
 netlink_unicast_kernel net/netlink/af_netlink.c:1335 [inline]
 netlink_unicast+0x58d/0x660 net/netlink/af_netlink.c:1361
 netlink_sendmsg+0x5ca/0x6e0 net/netlink/af_netlink.c:1905
 sock_sendmsg_nosec net/socket.c:730 [inline]
 __sock_sendmsg+0x140/0x180 net/socket.c:745
 ____sys_sendmsg+0x312/0x410 net/socket.c:2585
 ___sys_sendmsg net/socket.c:2639 [inline]
 __sys_sendmsg+0x1e9/0x280 net/socket.c:2668
 __do_sys_sendmsg net/socket.c:2677 [inline]
 __se_sys_sendmsg net/socket.c:2675 [inline]
 __x64_sys_sendmsg+0x46/0x50 net/socket.c:2675
 x64_sys_call+0xb25/0x2d70 arch/x86/include/generated/asm/syscalls_64.h:47
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888112d970b0 of 4 bytes by task 11 on cpu 1:
 netif_is_bond_master include/linux/netdevice.h:5020 [inline]
 is_upper_ndev_bond_master_filter+0x2b/0xb0 drivers/infiniband/core/roce_gid_mgmt.c:275
 ib_enum_roce_netdev+0x124/0x1d0 drivers/infiniband/core/device.c:2310
 ib_enum_all_roce_netdevs+0x8a/0x100 drivers/infiniband/core/device.c:2337
 netdevice_event_work_handler+0x15b/0x3c0 drivers/infiniband/core/roce_gid_mgmt.c:626
 process_one_work kernel/workqueue.c:3248 [inline]
 process_scheduled_works+0x483/0x9a0 kernel/workqueue.c:3329
 worker_thread+0x526/0x720 kernel/workqueue.c:3409
 kthread+0x1d1/0x210 kernel/kthread.c:389
 ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

value changed: 0x00001002 -> 0x00000202

According to KCSAN report, there is a read/write race between 
__dev_change_flags and netif_is_bond_master for dev->flags. Therefore, 
should change to use READ_ONCE() when reading dev->flags.

Reported-by: syzbot+113b65786d8662e21ff7@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 8a7fbfab4be3 ("netxen: write IP address to firmware when using bonding")
Signed-off-by: Jeongjun Park <aha310510@xxxxxxxxx>
---
 include/linux/netdevice.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 607009150b5f..5c95d7925b3f 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -5043,7 +5043,7 @@ static inline bool netif_is_macvlan_port(const struct net_device *dev)
 
 static inline bool netif_is_bond_master(const struct net_device *dev)
 {
-	return dev->flags & IFF_MASTER && dev->priv_flags & IFF_BONDING;
+	return READ_ONCE(dev->flags) & IFF_MASTER && dev->priv_flags & IFF_BONDING;
 }
 
 static inline bool netif_is_bond_slave(const struct net_device *dev)
--