Re: [PATCH] usb-core: Fix potential null pointer dereference in xhci-debugfs.c

[Mathias Nyman]

On 07.12.2017 11:26, Alexander Kappner wrote:
> Date: Wed, 6 Dec 2017 15:28:37 -0800
> Subject: [PATCH] usb-core: Fix potential null pointer dereference in xhci-debugfs.c

(Added this as reply subject, please remember to send mail with proper subject)

> My kernel crashed just after resuming from hibernate and starting usbmuxd
> (a user-space daemon for iOS device pairing) with several USB devices
> connected (dmesg attached).
>
> Backtrace leads to:
>
> 0xffffffff8170465d is in xhci_debugfs_create_endpoint
> (drivers/usb/host/xhci-debugfs.c:381).
> 376                                       int ep_index)
> 377     {
> 378             struct xhci_ep_priv     *epriv;
> 379             struct xhci_slot_priv   *spriv = dev->debugfs_private;
> 380
> 381             if (spriv->eps[ep_index])
> 382                     return;
> 383
> 384             epriv = kzalloc(sizeof(*epriv), GFP_KERNEL);
> 385             if (!epriv)
>
> The read violation happens at address 0x40 and sizeof(struct
> xhci_ep_priv)=0x40, so it seems ep_index is 1 and spriv is NULL here.

Thanks for reporting and debugging this, much appreciated.
 
> spriv gets allocated in xhci_debugfs_create_slot:
>
> ...
> priv = kzalloc(sizeof(*priv), GFP_KERNEL);
> if (!priv)
>      return;
> ...
>
> There's no separate error path if this allocation fails, so we might be
> left with NULL in priv. Subsequent users of priv thus need to check for
> this NULL - so this is what the patch does.

I think we need to dig a bit deeper. It's good to check if spriv is valid
but there are probably other reasons than kzalloc failing.

Resume from hibernation will reset the xhci controller, reinitializing a lot.
It could be related.

-Mathias

(keeping rest of message as reference)

> There might be other ways of triggering this null pointer dereference,
> including when xhci_resume frees the device structures (e.g. after
> returning from a hibernate), but I wasn't able to find or reproduce it.
>
> [63953.758083] BUG: unable to handle kernel NULL pointer dereference at
> 0000000000000040
> [63953.758090] IP: xhci_debugfs_create_endpoint+0x1d/0xa0
> [63953.758091] PGD bb911d067 P4D bb911d067 PUD 10500ff067 PMD 0
> [63953.758093] Oops: 0000 [#1] PREEMPT SMP
> [63953.758094] Modules linked in: ipheth tun nvidia_modeset(PO) iwlmvm
> mac80211 iwlwifi nvidia(PO) btusb btrtl btbcm btintel bluetooth cfg80211
> qmi_wwan ecdh_generic thinkpad_acpi rfkill
> [63953.758103] CPU: 4 PID: 27091 Comm: usbmuxd Tainted: P           O
> 4.14.0.1-12769-g1deab8c #1
> [63953.758104] Hardware name: LENOVO 20ENCTO1WW/20ENCTO1WW, BIOS N1EET62W
> (1.35 ) 11/10/2016
> [63953.758105] task: ffff8810527ba0c0 task.stack: ffffc9000a8ec000
> [63953.758107] RIP: 0010:xhci_debugfs_create_endpoint+0x1d/0xa0
> [63953.758108] RSP: 0018:ffffc9000a8efc80 EFLAGS: 00010206
> [63953.758109] RAX: 0000000000000000 RBX: ffff88105a71c000 RCX:
> 0000000000030000
> [63953.758110] RDX: 0000000000000003 RSI: ffff880c0b57e000 RDI:
> ffff88105a71c238
> [63953.758110] RBP: 0000000000000003 R08: ffff881063800600 R09:
> 0000000000000003
> [63953.758111] R10: ffff88105a71c238 R11: 0000000000000001 R12:
> 0000000000000011
> [63953.758112] R13: 0000000000000018 R14: 0000000000000000 R15:
> 0000000000000000
> [63953.758113] FS:  00007f0a77715700(0000) GS:ffff8810a3d00000(0000)
> knlGS:0000000000000000
> [63953.758114] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [63953.758115] CR2: 0000000000000040 CR3: 00000003f91a8006 CR4:
> 00000000003606e0
> [63953.758115] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
> 0000000000000000
> [63953.758116] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7:
> 0000000000000400
> [63953.758117] Call Trace:
> [63953.758120]  xhci_add_endpoint+0x127/0x2b0
> [63953.758123]  usb_hcd_alloc_bandwidth+0x1ad/0x300
> [63953.758125]  usb_set_configuration+0x1c8/0x880
> [63953.758128]  usbdev_do_ioctl+0xc41/0x1120
> [63953.758130]  usbdev_ioctl+0xa/0x10
> [63953.758151]  do_vfs_ioctl+0x8b/0x5c0
> [63953.758153]  ? __fget+0x6c/0xb0
> [63953.758155]  SyS_ioctl+0x76/0x90
> [63953.758157]  do_syscall_64+0x6b/0x290
> [63953.758173]  entry_SYSCALL64_slow_path+0x25/0x25
> [63953.758175] RIP: 0033:0x7f0a76a151c7
> [63953.758175] RSP: 002b:00007ffd1431b0c8 EFLAGS: 00000202 ORIG_RAX:
> 0000000000000010
> [63953.758177] RAX: ffffffffffffffda RBX: 00000000023239a0 RCX:
> 00007f0a76a151c7
> [63953.758178] RDX: 00007ffd1431b0dc RSI: 0000000080045505 RDI:
> 000000000000000e
> [63953.758178] RBP: 00000000023240c0 R08: 00007ffd1431b008 R09:
> 0000000000000004
> [63953.758179] R10: 00007ffd1431aec0 R11: 0000000000000202 R12:
> 00000000023240c0
> [63953.758180] R13: 0000000000000001 R14: 0000000000000056 R15:
> 0000000000000038
> [63953.758182] Code: e9 39 ff ff ff 66 0f 1f 84 00 00 00 00 00 0f 1f 44 00
> 00 41 57 41 56 41 55 41 54 55 48 63 ea 53 4c 8b b6 88 15 00 00 4d 8d 2c ee
> <49> 83 7d 28 00 74 0b 5b 5d 41 5c 41 5d 41 5e 41 5f c3 48 8b 3d
> [63953.758202] RIP: xhci_debugfs_create_endpoint+0x1d/0xa0 RSP:
> ffffc9000a8efc80
> [63953.758203] CR2: 0000000000000040
> [63953.758204] ---[ end trace 1f7ea9a959f02054 ]---
>
> Signed-off-by: Alexander Kappner <agk@xxxxxxxxxxx>
> ---
>   drivers/usb/host/xhci-debugfs.c | 3 +++
>   1 file changed, 3 insertions(+)
>
> diff --git a/drivers/usb/host/xhci-debugfs.c b/drivers/usb/host/xhci-debugfs.c
> index 4f7895d..1cea59c 100644
> --- a/drivers/usb/host/xhci-debugfs.c
> +++ b/drivers/usb/host/xhci-debugfs.c
> @@ -378,6 +378,9 @@ void xhci_debugfs_create_endpoint(struct xhci_hcd *xhci,
>   	struct xhci_ep_priv	*epriv;
>   	struct xhci_slot_priv	*spriv = dev->debugfs_private;
>   
> +	if (!spriv)
> +		return;
> +
>   	if (spriv->eps[ep_index])
>   		return;
>