vlan: fix memory leak in vlan_newlink()

Blamed commit added back a bug I fixed in commit 9bbd917e
("vlan: fix memory leak in vlan_dev_set_egress_priority")

If a memory allocation fails in vlan_changelink() after other allocations
succeeded, we need to call vlan_dev_free_egress_priority()
to free all allocated memory because after a failed ->newlink()
we do not call any methods like ndo_uninit() or dev->priv_destructor().

In following example, if the allocation for last element 2000:2001 fails,
we need to free eight prior allocations:

ip link add link dummy0 dummy0.100 type vlan id 100 \
	egress-qos-map 1:2 2:3 3:4 4:5 5:6 6:7 7:8 8:9 2000:2001

syzbot report was:

BUG: memory leak
unreferenced object 0xffff888117bd1060 (size 32):
comm "syz-executor408", pid 3759, jiffies 4294956555 (age 34.090s)
hex dump (first 32 bytes):
09 00 00 00 00 a0 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
backtrace:
[<ffffffff83fc60ad>] kmalloc include/linux/slab.h:600 [inline]
[<ffffffff83fc60ad>] vlan_dev_set_egress_priority+0xed/0x170 net/8021q/vlan_dev.c:193
[<ffffffff83fc6628>] vlan_changelink+0x178/0x1d0 net/8021q/vlan_netlink.c:128
[<ffffffff83fc67c8>] vlan_newlink+0x148/0x260 net/8021q/vlan_netlink.c:185
[<ffffffff838b1278>] rtnl_newlink_create net/core/rtnetlink.c:3363 [inline]
[<ffffffff838b1278>] __rtnl_newlink+0xa58/0xdc0 net/core/rtnetlink.c:3580
[<ffffffff838b1629>] rtnl_newlink+0x49/0x70 net/core/rtnetlink.c:3593
[<ffffffff838ac66c>] rtnetlink_rcv_msg+0x21c/0x5c0 net/core/rtnetlink.c:6089
[<ffffffff839f9c37>] netlink_rcv_skb+0x87/0x1d0 net/netlink/af_netlink.c:2501
[<ffffffff839f8da7>] netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
[<ffffffff839f8da7>] netlink_unicast+0x397/0x4c0 net/netlink/af_netlink.c:1345
[<ffffffff839f9266>] netlink_sendmsg+0x396/0x710 net/netlink/af_netlink.c:1921
[<ffffffff8384dbf6>] sock_sendmsg_nosec net/socket.c:714 [inline]
[<ffffffff8384dbf6>] sock_sendmsg+0x56/0x80 net/socket.c:734
[<ffffffff8384e15c>] ____sys_sendmsg+0x36c/0x390 net/socket.c:2488
[<ffffffff838523cb>] ___sys_sendmsg+0x8b/0xd0 net/socket.c:2542
[<ffffffff838525b8>] __sys_sendmsg net/socket.c:2571 [inline]
[<ffffffff838525b8>] __do_sys_sendmsg net/socket.c:2580 [inline]
[<ffffffff838525b8>] __se_sys_sendmsg net/socket.c:2578 [inline]
[<ffffffff838525b8>] __x64_sys_sendmsg+0x78/0xf0 net/socket.c:2578
[<ffffffff845ad8d5>] do_syscall_x64 arch/x86/entry/common.c:50 [inline]
[<ffffffff845ad8d5>] do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
[<ffffffff8460006a>] entry_SYSCALL_64_after_hwframe+0x46/0xb0

Fixes: 37aa50c5 ("vlan: introduce vlan_dev_free_egress_priority")
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Xin Long <lucien.xin@gmail.com>
Reviewed-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/8021q/vlan_netlink.c

@@ -182,10 +182,14 @@ static int vlan_newlink(struct net *src_net, struct net_device *dev,
 	else if (dev->mtu > max_mtu)
 		return -EINVAL;
 
+	/* Note: If this initial vlan_changelink() fails, we need
+	 * to call vlan_dev_free_egress_priority() to free memory.
+	 */
 	err = vlan_changelink(dev, tb, data, extack);
-	if (err)
-		return err;
-	err = register_vlan_dev(dev, extack);
+
+	if (!err)
+		err = register_vlan_dev(dev, extack);
+
 	if (err)
 		vlan_dev_free_egress_priority(dev);
 	return err;