Re: [PATCH net] netfilter: x_tables: fix missing timer initialization in xt_LED

[Dmitry Vyukov <dvyukov@google.com>]

On Mon, Feb 12, 2018 at 6:17 PM, Paolo Abeni <pabeni@redhat.com> wrote:
> syzbot reported that xt_LED may try to use the ledinternal->timer
> without previously initializing it:
>
> ------------[ cut here ]------------
> kernel BUG at kernel/time/timer.c:958!
> invalid opcode: 0000 [#1] SMP KASAN
> Dumping ftrace buffer:
>     (ftrace buffer empty)
> Modules linked in:
> CPU: 1 PID: 1826 Comm: kworker/1:2 Not tainted 4.15.0+ #306
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Workqueue: ipv6_addrconf addrconf_dad_work
> RIP: 0010:__mod_timer kernel/time/timer.c:958 [inline]
> RIP: 0010:mod_timer+0x7d6/0x13c0 kernel/time/timer.c:1102
> RSP: 0018:ffff8801d24fe9f8 EFLAGS: 00010293
> RAX: ffff8801d25246c0 RBX: ffff8801aec6cb50 RCX: ffffffff816052c6
> RDX: 0000000000000000 RSI: 00000000fffbd14b RDI: ffff8801aec6cb68
> RBP: ffff8801d24fec98 R08: 0000000000000000 R09: 1ffff1003a49fd6c
> R10: ffff8801d24feb28 R11: 0000000000000005 R12: dffffc0000000000
> R13: ffff8801d24fec70 R14: 00000000fffbd14b R15: ffff8801af608f90
> FS:  0000000000000000(0000) GS:ffff8801db500000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00000000206d6fd0 CR3: 0000000006a22001 CR4: 00000000001606e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>   led_tg+0x1db/0x2e0 net/netfilter/xt_LED.c:75
>   ip6t_do_table+0xc2a/0x1a30 net/ipv6/netfilter/ip6_tables.c:365
>   ip6table_raw_hook+0x65/0x80 net/ipv6/netfilter/ip6table_raw.c:42
>   nf_hook_entry_hookfn include/linux/netfilter.h:120 [inline]
>   nf_hook_slow+0xba/0x1a0 net/netfilter/core.c:483
>   nf_hook.constprop.27+0x3f6/0x830 include/linux/netfilter.h:243
>   NF_HOOK include/linux/netfilter.h:286 [inline]
>   ndisc_send_skb+0xa51/0x1370 net/ipv6/ndisc.c:491
>   ndisc_send_ns+0x38a/0x870 net/ipv6/ndisc.c:633
>   addrconf_dad_work+0xb9e/0x1320 net/ipv6/addrconf.c:4008
>   process_one_work+0xbbf/0x1af0 kernel/workqueue.c:2113
>   worker_thread+0x223/0x1990 kernel/workqueue.c:2247
>   kthread+0x33c/0x400 kernel/kthread.c:238
>   ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:429
> Code: 85 2a 0b 00 00 4d 8b 3c 24 4d 85 ff 75 9f 4c 8b bd 60 fd ff ff e8 bb
> 57 10 00 65 ff 0d 94 9a a1 7e e9 d9 fc ff ff e8 aa 57 10 00 <0f> 0b e8 a3
> 57 10 00 e9 14 fb ff ff e8 99 57 10 00 4c 89 bd 70
> RIP: __mod_timer kernel/time/timer.c:958 [inline] RSP: ffff8801d24fe9f8
> RIP: mod_timer+0x7d6/0x13c0 kernel/time/timer.c:1102 RSP: ffff8801d24fe9f8
> ---[ end trace f661ab06f5dd8b3d ]---
>
> The ledinternal struct can be shared between several different
> xt_LED targets, but the related timer is currently initialized only
> if the first target requires it. Fix it by unconditionally
> initializing the timer struct.
>
> Fixes: 268cb38e1802 ("netfilter: x_tables: add LED trigger target")
> Reported-by: syzbot+10c98dc5725c6c8fc7fb@syzkaller.appspotmail.com
> Signed-off-by: Paolo Abeni <pabeni@redhat.com>
> ---
>  net/netfilter/xt_LED.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/net/netfilter/xt_LED.c b/net/netfilter/xt_LED.c
> index 1dcad893df78..87c90d7ebec0 100644
> --- a/net/netfilter/xt_LED.c
> +++ b/net/netfilter/xt_LED.c
> @@ -142,9 +142,10 @@ static int led_tg_check(const struct xt_tgchk_param *par)
>                 goto exit_alloc;
>         }
>
> -       /* See if we need to set up a timer */
> -       if (ledinfo->delay > 0)
> -               timer_setup(&ledinternal->timer, led_timeout_callback, 0);
> +       /* Since the letinternal timer can be shared between multiple targets,
> +        * always set it up, even if the current target does not need it
> +        */
> +       timer_setup(&ledinternal->timer, led_timeout_callback, 0);

Shouldn't this also make del_timer_sync() unconditional?

>         list_add_tail(&ledinternal->list, &xt_led_triggers);
>
> --
> 2.14.3
>
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