memory leak in garp_request_join

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    d5226fa6 Linux 5.5
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=176b440de00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=698d5ad38dda6cb6
dashboard link: https://syzkaller.appspot.com/bug?extid=13ad608e190b5f8ad8a8
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15d86b35e00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1043d769e00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+13ad608e190b5f8ad8a8@xxxxxxxxxxxxxxxxxxxxxxxxx

BUG: memory leak
unreferenced object 0xffff888114008dc0 (size 64):
  comm "syz-executor967", pid 7318, jiffies 4294943348 (age 13.580s)
  hex dump (first 32 bytes):
    01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    00 00 00 00 00 00 00 00 08 00 00 00 01 02 00 08  ................
  backtrace:
    [<0000000067139221>] kmemleak_alloc_recursive include/linux/kmemleak.h:43 [inline]
    [<0000000067139221>] slab_post_alloc_hook mm/slab.h:586 [inline]
    [<0000000067139221>] slab_alloc mm/slab.c:3320 [inline]
    [<0000000067139221>] __do_kmalloc mm/slab.c:3654 [inline]
    [<0000000067139221>] __kmalloc+0x169/0x300 mm/slab.c:3665
    [<0000000093813bfa>] kmalloc include/linux/slab.h:561 [inline]
    [<0000000093813bfa>] garp_attr_create net/802/garp.c:187 [inline]
    [<0000000093813bfa>] garp_request_join+0x132/0x1f0 net/802/garp.c:350
    [<0000000078a2be7e>] vlan_gvrp_request_join+0x86/0x90 net/8021q/vlan_gvrp.c:34
    [<0000000092861d25>] vlan_dev_open+0x173/0x290 net/8021q/vlan_dev.c:290
    [<00000000451be632>] __dev_open+0x109/0x1b0 net/core/dev.c:1431
    [<00000000fa297b7f>] __dev_change_flags+0x246/0x2c0 net/core/dev.c:8105
    [<0000000065bc5439>] rtnl_configure_link+0x57/0x100 net/core/rtnetlink.c:2996
    [<000000005ed66308>] __rtnl_newlink+0x8b9/0xb80 net/core/rtnetlink.c:3332
    [<00000000d6be140e>] rtnl_newlink+0x4e/0x80 net/core/rtnetlink.c:3372
    [<0000000030786841>] rtnetlink_rcv_msg+0x178/0x4b0 net/core/rtnetlink.c:5433
    [<00000000cb252134>] netlink_rcv_skb+0x61/0x170 net/netlink/af_netlink.c:2477
    [<000000002c0f0d61>] rtnetlink_rcv+0x1d/0x30 net/core/rtnetlink.c:5451
    [<00000000e09dee2f>] netlink_unicast_kernel net/netlink/af_netlink.c:1302 [inline]
    [<00000000e09dee2f>] netlink_unicast+0x223/0x310 net/netlink/af_netlink.c:1328
    [<0000000036f4d1c5>] netlink_sendmsg+0x2c0/0x570 net/netlink/af_netlink.c:1917
    [<0000000064dc927c>] sock_sendmsg_nosec net/socket.c:639 [inline]
    [<0000000064dc927c>] sock_sendmsg+0x54/0x70 net/socket.c:659
    [<00000000cd57f12f>] ____sys_sendmsg+0x2d0/0x300 net/socket.c:2330



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