net_sched: fix an oops in tcindex filter

net_sched: fix an oops in tcindex filter

Kelly reported the following crash:

        IP: [<ffffffff817a993d>] tcf_action_exec+0x46/0x90
        PGD 3009067 PUD 300c067 PMD 11ff30067 PTE 800000011634b060
        Oops: 0000 [#1] SMP DEBUG_PAGEALLOC
        CPU: 1 PID: 639 Comm: dhclient Not tainted 3.15.0-rc4+ #342
        Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
        task: ffff8801169ecd00 ti: ffff8800d21b8000 task.ti: ffff8800d21b8000
        RIP: 0010:[<ffffffff817a993d>]  [<ffffffff817a993d>] tcf_action_exec+0x46/0x90
        RSP: 0018:ffff8800d21b9b90  EFLAGS: 00010283
        RAX: 00000000ffffffff RBX: ffff88011634b8e8 RCX: ffff8800cf7133d8
        RDX: ffff88011634b900 RSI: ffff8800cf7133e0 RDI: ffff8800d210f840
        RBP: ffff8800d21b9bb0 R08: ffffffff8287bf60 R09: 0000000000000001
        R10: ffff8800d2b22b24 R11: 0000000000000001 R12: ffff8800d210f840
        R13: ffff8800d21b9c50 R14: ffff8800cf7133e0 R15: ffff8800cad433d8
        FS:  00007f49723e1840(0000) GS:ffff88011a800000(0000) knlGS:0000000000000000
        CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
        CR2: ffff88011634b8f0 CR3: 00000000ce469000 CR4: 00000000000006e0
        Stack:
         ffff8800d2170188 ffff8800d210f840 ffff8800d2171b90 0000000000000000
         ffff8800d21b9be8 ffffffff817c55bb ffff8800d21b9c50 ffff8800d2171b90
         ffff8800d210f840 ffff8800d21b0300 ffff8800d21b9c50 ffff8800d21b9c18
        Call Trace:
         [<ffffffff817c55bb>] tcindex_classify+0x88/0x9b
         [<ffffffff817a7f7d>] tc_classify_compat+0x3e/0x7b
         [<ffffffff817a7fdf>] tc_classify+0x25/0x9f
         [<ffffffff817b0e68>] htb_enqueue+0x55/0x27a
         [<ffffffff817b6c2e>] dsmark_enqueue+0x165/0x1a4
         [<ffffffff81775642>] __dev_queue_xmit+0x35e/0x536
         [<ffffffff8177582a>] dev_queue_xmit+0x10/0x12
         [<ffffffff818f8ecd>] packet_sendmsg+0xb26/0xb9a
         [<ffffffff810b1507>] ? __lock_acquire+0x3ae/0xdf3
         [<ffffffff8175cf08>] __sock_sendmsg_nosec+0x25/0x27
         [<ffffffff8175d916>] sock_aio_write+0xd0/0xe7
         [<ffffffff8117d6b8>] do_sync_write+0x59/0x78
         [<ffffffff8117d84d>] vfs_write+0xb5/0x10a
         [<ffffffff8117d96a>] SyS_write+0x49/0x7f
         [<ffffffff8198e212>] system_call_fastpath+0x16/0x1b

This is because we memcpy struct tcindex_filter_result which contains
struct tcf_exts, obviously struct list_head can not be simply copied.
This is a regression introduced by commit 33be627159913b094bb578
(net_sched: act: use standard struct list_head).

It's not very easy to fix it as the code is a mess:

       if (old_r)
               memcpy(&cr, r, sizeof(cr));
       else {
               memset(&cr, 0, sizeof(cr));
               tcf_exts_init(&cr.exts, TCA_TCINDEX_ACT, TCA_TCINDEX_POLICE);
       }
       ...
       tcf_exts_change(tp, &cr.exts, &e);
       ...
       memcpy(r, &cr, sizeof(cr));

the above code should equal to:

        tcindex_filter_result_init(&cr);
        if (old_r)
               cr.res = r->res;
        ...
        if (old_r)
               tcf_exts_change(tp, &r->exts, &e);
        else
               tcf_exts_change(tp, &cr.exts, &e);
        ...
        r->res = cr.res;

after this change, since there is no need to copy struct tcf_exts.

And it also fixes other places zero'ing struct's contains struct tcf_exts.

Fixes: commit 33be627159913b0 (net_sched: act: use standard struct list_head)
Reported-by: Kelly Anderson <kelly@xilka.com>
Tested-by: Kelly Anderson <kelly@xilka.com>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>