memory leak in ctnetlink_start

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    7ae77150 Merge tag 'powerpc-5.8-1' of git://git.kernel.org..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=128a9df2100000
kernel config:  https://syzkaller.appspot.com/x/.config?x=9a1aa05456dfd557
dashboard link: https://syzkaller.appspot.com/bug?extid=b005af2cfb0411e617de
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=17304a96100000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=168a9df2100000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+b005af2cfb0411e617de@xxxxxxxxxxxxxxxxxxxxxxxxx

executing program
executing program
executing program
BUG: memory leak
unreferenced object 0xffff88811c797900 (size 128):
  comm "syz-executor256", pid 6458, jiffies 4294947022 (age 13.050s)
  hex dump (first 32 bytes):
    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 00 00 00 00 00 00  ................
  backtrace:
    [<000000004276332a>] kmalloc include/linux/slab.h:555 [inline]
    [<000000004276332a>] kzalloc include/linux/slab.h:669 [inline]
    [<000000004276332a>] ctnetlink_alloc_filter+0x3a/0x2a0 net/netfilter/nf_conntrack_netlink.c:924
    [<000000000047e6fb>] ctnetlink_start+0x3a/0x80 net/netfilter/nf_conntrack_netlink.c:998
    [<00000000a431a924>] __netlink_dump_start+0x1a3/0x2e0 net/netlink/af_netlink.c:2343
    [<0000000016b073fa>] netlink_dump_start include/linux/netlink.h:246 [inline]
    [<0000000016b073fa>] ctnetlink_get_conntrack+0x26d/0x2f0 net/netfilter/nf_conntrack_netlink.c:1611
    [<00000000d311138b>] nfnetlink_rcv_msg+0x32f/0x370 net/netfilter/nfnetlink.c:229
    [<0000000008feca87>] netlink_rcv_skb+0x5a/0x180 net/netlink/af_netlink.c:2469
    [<0000000088caad78>] nfnetlink_rcv+0x83/0x1b0 net/netfilter/nfnetlink.c:563
    [<0000000052160488>] netlink_unicast_kernel net/netlink/af_netlink.c:1303 [inline]
    [<0000000052160488>] netlink_unicast+0x20a/0x2f0 net/netlink/af_netlink.c:1329
    [<00000000ee36d991>] netlink_sendmsg+0x2b5/0x560 net/netlink/af_netlink.c:1918
    [<00000000dee2cafe>] sock_sendmsg_nosec net/socket.c:652 [inline]
    [<00000000dee2cafe>] sock_sendmsg+0x4c/0x60 net/socket.c:672
    [<00000000b0b655cb>] ____sys_sendmsg+0x2c4/0x2f0 net/socket.c:2352
    [<000000005bba2f8d>] ___sys_sendmsg+0x8a/0xd0 net/socket.c:2406
    [<0000000060ac6563>] __sys_sendmsg+0x77/0xe0 net/socket.c:2439
    [<000000002f7b34b0>] do_syscall_64+0x6e/0x220 arch/x86/entry/common.c:295
    [<00000000941009bb>] entry_SYSCALL_64_after_hwframe+0x44/0xa9



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