Re: [PATCH] xhci: Fix use-after-free in xhci debugfs

[Mathias Nyman]

On 11.12.2017 00:14, Alexander Kappner wrote:
> Trying to read from debugfs after the system has resumed from
>   hibernate causes a use-after-free and thus a protection fault.
>
> Steps to reproduce:
> Hibernate system, resume from hibernate, then run
> $ cat /sys/kernel/debug/usb/xhci/*/command-ring/enqueue
>
> dmesg below:
>
> [ 3902.765086] general protection fault: 0000 [#1] PREEMPT SMP
> [ 3902.765095] Modules linked in: ipheth nvidia_modeset(PO) iwlmvm mac80211 nvidia(PO) iwlwifi qmi_wwan cfg80211 thinkpad_acpi rfkill
> [ 3902.765118] CPU: 4 PID: 3591 Comm: cat Tainted: P           O     4.14.0.1-12769-g1deab8c #1
> [ 3902.765121] Hardware name: LENOVO 20ENCTO1WW/20ENCTO1WW, BIOS N1EET62W (1.35 ) 11/10/2016
> [ 3902.765125] task: ffff88100263d040 task.stack: ffffc90006e50000
> [ 3902.765136] RIP: 0010:xhci_trb_virt_to_dma.part.50+0x5/0x30
> [ 3902.765140] RSP: 0018:ffffc90006e53da8 EFLAGS: 00010286
> [ 3902.765144] RAX: ffff88100a57e680 RBX: ffff8810032f1900 RCX: ffff881013800900
> [ 3902.765147] RDX: 0000000000000000 RSI: ffff881000abf488 RDI: 0d0c0a0bb1637008
> [ 3902.765151] RBP: ffffc90006e53f00 R08: 0000000000000000 R09: 0000000000000000
> [ 3902.765154] R10: 00007ffcd73165e0 R11: ffff88100263d040 R12: ffff880bd5afcc00
> [ 3902.765157] R13: 0000000000020000 R14: 0000000000000001 R15: ffff8810032f1900
> [ 3902.765161] FS:  00007f6aa6cec700(0000) GS:ffff881053d00000(0000) knlGS:0000000000000000
> [ 3902.765165] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 3902.765168] CR2: 00007f6aa6d08008 CR3: 00000010033f9003 CR4: 00000000003606e0
> [ 3902.765172] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [ 3902.765175] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> [ 3902.765178] Call Trace:
> [ 3902.765188]  xhci_ring_enqueue_show+0x1e/0x40
> [ 3902.765197]  seq_read+0xdb/0x3a0
> [ 3902.765204]  ? __handle_mm_fault+0x5fb/0x1210
> [ 3902.765211]  full_proxy_read+0x4a/0x70
> [ 3902.765219]  __vfs_read+0x23/0x120
> [ 3902.765228]  vfs_read+0x8e/0x130
> [ 3902.765235]  SyS_read+0x42/0x90
> [ 3902.765242]  do_syscall_64+0x6b/0x290
> [ 3902.765251]  entry_SYSCALL64_slow_path+0x25/0x25
> [ 3902.765256] RIP: 0033:0x7f6aa683cba0
> [ 3902.765260] RSP: 002b:00007ffcd7316818 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
> [ 3902.765264] RAX: ffffffffffffffda RBX: 0000000000020000 RCX: 00007f6aa683cba0
> [ 3902.765267] RDX: 0000000000020000 RSI: 00007f6aa6d09000 RDI: 0000000000000003
> [ 3902.765270] RBP: 0000000000020000 R08: 00000000ffffffff R09: 0000000000000000
> [ 3902.765274] R10: 00007ffcd73165e0 R11: 0000000000000246 R12: 00007f6aa6d09000
> [ 3902.765277] R13: 0000000000000003 R14: 0000000000000000 R15: 0000000000020000
> [ 3902.765282] Code: 0f 44 c0 49 8b 04 24 52 48 c7 c2 30 cd cb 81 48 8d b0 98 00 00 00 31 c0 e8 39 e6 dc ff 58 e9 75 ff ff ff 0f 1f 00 0f 1f 44 00 00 <48> 8b 17 31 c0 48 39 f2 77 13 48 29 d6 48 81 fe ff 0f 00 00 77
> [ 3902.765371] RIP: xhci_trb_virt_to_dma.part.50+0x5/0x30 RSP: ffffc90006e53da8
> [ 3902.765376] ---[ end trace 9ee53de1dccf7d8e ]---
>
> The issue is caused by the xhci ring structures being reallocated
> when the system is resumed, but pointers to the old structures
> being retained in the debugfs files "private" field:
>
> (gdb) list *(xhci_ring_enqueue_show+0x1e)
> 0xffffffff8170403e is in xhci_ring_enqueue_show (drivers/usb/host/xhci-debugfs.c:168).
> 163	{
> 164		dma_addr_t		dma;
> 165		struct xhci_ring	*ring = s->private;
> 166
> 167		dma = xhci_trb_virt_to_dma(ring->enq_seg, ring->enqueue);
> 168		seq_printf(s, "%pad\n", &dma);
> 169
> 170		return 0;
> 171	}
> 172
>
> The proposed patch fixes this issue by storing a pointer to the xhci_ring
> field in the xhci device structure in debugfs rather than directly
> storing a pointer to the xhci_ring.
>
> Signed-off-by: Alexander Kappner <agk@xxxxxxxxxxx>
> ---

Thanks, that should work.
I'll try it out, and shorten the commit message a bit.
If everything works I'll apply it to my for-usb-linus branch

-Mathias