linux-kernel - Re: tip -ENOBOOT - bisected to locking/refcounts, x86/asm: Implement fast refcount overflow protection

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Date:   Wed, 30 Aug 2017 19:27:26 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Mike Galbraith <efault@....de>
Cc:     LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
        "Reshetova, Elena" <elena.reshetova@...el.com>
Subject: Re: tip -ENOBOOT - bisected to locking/refcounts, x86/asm: Implement
 fast refcount overflow protection

On Wed, Aug 30, 2017 at 7:09 PM, Mike Galbraith <efault@....de> wrote:
> On Wed, 2017-08-30 at 12:46 -0700, Kees Cook wrote:
>>
>> With CONFIG_ARCH_HAS_REFCOUNT=y and this patch, do you get an earlier splat?
>
> Yup, first gripe below.
>
> [    2.448393] refcount_t silent saturation at skb_unref.part.36+0x12/0x1a in (haveged)[136], uid/euid: 0/0
> [    2.454975] ------------[ cut here ]------------
> [    2.456452] WARNING: CPU: 1 PID: 136 at kernel/panic.c:612 refcount_error_report+0xa0/0xa4
> [    2.456452] Modules linked in: scsi_mod(E+) autofs4(E)
> [    2.456456] CPU: 1 PID: 136 Comm: (haveged) Tainted: G            E   4.13.0.g152d54a-tip-default #47
> [    2.456456] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.0.0-prebuilt.qemu-project.org 04/01/2014
> [    2.456457] task: ffff880137f65640 task.stack: ffffc9000093c000
> [    2.456458] RIP: 0010:refcount_error_report+0xa0/0xa4
> [    2.456459] RSP: 0018:ffffc9000093fa38 EFLAGS: 00010282
> [    2.456459] RAX: 000000000000005c RBX: ffffffff81a33864 RCX: 0000000000000830
> [    2.456459] RDX: 0000000000000001 RSI: 0000000000000082 RDI: 0000000000000246
> [    2.456460] RBP: ffffc9000093fb88 R08: 000000008e8d4f61 R09: 0000000000000000
> [    2.456462] R10: 0000000000000000 R11: ffff880137f61600 R12: ffff880137f65640
> [    2.456463] R13: 0000000000000000 R14: 0000000000000004 R15: 0000000000000006
> [    2.456464] FS:  00007f5a33a14880(0000) GS:ffff88013fd00000(0000) knlGS:0000000000000000
> [    2.456464] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [    2.456464] CR2: 00007ffe37ca0c88 CR3: 0000000137f74005 CR4: 00000000001606e0
> [    2.456467] Call Trace:
> [    2.456478]  ex_handler_refcount+0x63/0x70
> [    2.456479]  fixup_exception+0x32/0x40
> [    2.456482]  do_trap+0x11b/0x180
> [    2.456493]  do_error_trap+0x70/0xd0
> [    2.456497]  ? skb_unref.part.36+0x10/0x1a
> [    2.456502]  ? idr_get_free+0xcb/0x2f0
> [    2.456505]  invalid_op+0x1e/0x30
> [    2.456510] RIP: 0010:skb_unref.part.36+0x12/0x1a
> [    2.456510] RSP: 0018:ffffc9000093fc30 EFLAGS: 00010202
> [    2.456510] RAX: 0000000000000002 RBX: 0000000000000000 RCX: ffff880137df9ee4
> [    2.456511] RDX: ffff880137df0518 RSI: ffff880137df9e00 RDI: ffff880137df9e00
> [    2.456511] RBP: ffff880137df9e00 R08: ffff880137e30018 R09: ffffffff816b91f0
> [    2.456511] R10: 0000000000000017 R11: 00000000fffffff4 R12: 0000000000000000
> [    2.456512] R13: ffff88013a4e9000 R14: 0000000000000000 R15: ffff880137e30000
> [    2.456513]  ? cleanup_uevent_env+0x10/0x10
> [    2.456520]  kfree_skb+0x3f/0xa0
> [    2.456525]  netlink_broadcast_filtered+0x2c8/0x420
> [    2.456530]  ? cleanup_uevent_env+0x10/0x10
> [    2.456531]  kobject_uevent_env+0x476/0x650
> [    2.456540]  device_add+0x41e/0x5f0
> [    2.456550]  netdev_register_kobject+0x8e/0x170
> [    2.456553]  register_netdevice+0x27a/0x3d0
> [    2.456557]  register_netdev+0x16/0x30
> [    2.456562]  loopback_net_init+0x48/0xa0
> [    2.456567]  ops_init+0x39/0x110
> [    2.456568]  setup_net+0x85/0x130
> [    2.456569]  copy_net_ns+0xb9/0x1f0
> [    2.456571]  create_new_namespaces+0x11a/0x1b0
> [    2.456577]  unshare_nsproxy_namespaces+0x55/0xa0
> [    2.456578]  SyS_unshare+0x18d/0x330
> [    2.456581]  entry_SYSCALL_64_fastpath+0x1a/0xa5
> [    2.456584] RIP: 0033:0x7f5a320669f7
> [    2.456585] RSP: 002b:00007ffcd1e10908 EFLAGS: 00000246 ORIG_RAX: 0000000000000110
> [    2.456585] RAX: ffffffffffffffda RBX: 000000000159ae48 RCX: 00007f5a320669f7
> [    2.456586] RDX: 000000000000000b RSI: 00007ffcd1e10910 RDI: 0000000040000000
> [    2.456588] RBP: 00007ffcd1e10cf0 R08: 0000000000000001 R09: 00000000015b8d20
> [    2.456588] R10: 0000000000000022 R11: 0000000000000246 R12: 0000000000000000
> [    2.456588] R13: 00000000ffffffff R14: 00000000ffffffff R15: 0000000000000000
> [    2.456589] Code: 10 09 00 00 48 8b 95 80 00 00 00 49 8d 8c 24 f0 0a 00 00 41 89 c1 44 89 2c 24 48 89 de 48 c7 c7 80 70 a3 81 31 c0 e8 bd f1 05 00 <0f> ff eb 88 0f 1f 44 00 00 55 48 89 e5 41 56 41 55 41 54 49 89
> [    2.456599] ---[ end trace d3215cc8334d8520 ]---

Interesting! Can you try with 633547973ffc3 ("net: convert
sk_buff.users from atomic_t to refcount_t") reverted? I'll see if
running haveged will help me trigger this on my system...

-Kees

-- 
Kees Cook
Pixel Security