netdev - [PATCH] bonding: allow nesting of bonding device

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Message-ID: <20210623032108.51472-1-zhudi21@huawei.com>
Date:   Wed, 23 Jun 2021 11:21:08 +0800
From:   zhudi <zhudi21@...wei.com>
To:     <j.vosburgh@...il.com>, <vfalico@...il.com>, <kuba@...nel.org>,
        <davem@...emloft.net>, <eric.dumazet@...il.com>
CC:     <netdev@...r.kernel.org>, <zhudi21@...wei.com>,
        <rose.chen@...wei.com>, Jay Vosburgh <jay.vosburgh@...onical.com>
Subject: [PATCH] bonding: allow nesting of bonding device

From: Di Zhu <zhudi21@...wei.com>

The commit 3c9ef511b9fa ("bonding: avoid adding slave device with
IFF_MASTER flag") fix a crash when add slave device with IFF_MASTER,
but it rejects the scenario of nested bonding device.

As Eric Dumazet described: since there indeed is a usage scenario about
nesting bonding, we should not break it.

So we add a new judgment condition to allow nesting of bonding device.

Fixes: 3c9ef511b9fa ("bonding: avoid adding slave device with IFF_MASTER flag")
Suggested-by: Jay Vosburgh <jay.vosburgh@...onical.com>
Signed-off-by: Di Zhu <zhudi21@...wei.com>
---
 drivers/net/bonding/bond_main.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index 16840c9bc00d..03b1a93d7fea 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -1601,7 +1601,9 @@ int bond_enslave(struct net_device *bond_dev, struct net_device *slave_dev,
 	int link_reporting;
 	int res = 0, i;
 
-	if (slave_dev->flags & IFF_MASTER) {
+	if (slave_dev->flags & IFF_MASTER &&
+	    !netif_is_bond_master(slave_dev)) {
+		NL_SET_ERR_MSG(extack, "Device with IFF_MASTER cannot be enslaved");
 		netdev_err(bond_dev,
 			   "Error: Device with IFF_MASTER cannot be enslaved\n");
 		return -EPERM;
-- 
2.23.0