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Date:   Thu,  7 Dec 2017 01:26:14 -0800
From:   Alexander Kappner <agk@...king.net>
To:     mathias.nyman@...el.com,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Alexander Kappner <agk@...king.net>
Subject: 

Date: Wed, 6 Dec 2017 15:28:37 -0800
Subject: [PATCH] usb-core: Fix potential null pointer dereference in xhci-debugfs.c

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.

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.

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@...king.net>
---
 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;
 
-- 
2.1.4